Patent Publication Number: US-2022233174-A1

Title: Ultrasound device circuitry including phase-locked loop circuitry and methods of operating the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit under 35 U.S.C. § 119(e) of U.S. Patent Application Ser. No. 63/142,993, filed Jan. 28, 2021 under Attorney Docket No. B1348.70191US00, and entitled “ULTRASOUND DEVICE CIRCUITRY INCLUDING PHASE-LOCKED LOOP CIRCUITRY AND METHODS OF OPERATING THE SAME,” which is hereby incorporated by reference herein in its entirety. 
    
    
     FIELD 
     Generally, the aspects of the technology described herein relate to circuitry in ultrasound devices and methods of operating such circuitry. Certain aspects relate to phase-locked loop circuitry and methods of operating such circuitry. 
     BACKGROUND 
     Ultrasound probes may be used to perform diagnostic imaging and/or treatment, using sound waves with frequencies that are higher than those audible to humans. Ultrasound imaging may be used to see internal soft tissue body structures. When pulses of ultrasound are transmitted into tissue, sound waves of different amplitudes may be reflected back towards the probe at different tissue interfaces. These reflected sound waves may then be recorded and displayed as an image to the operator. The strength (amplitude) of the sound signal and the time it takes for the wave to travel through the body may provide information used to produce the ultrasound image. Many different types of images can be formed using ultrasound devices. For example, images can be generated that show two-dimensional cross-sections of tissue, blood flow, motion of tissue over time, the location of blood, the presence of specific molecules, the stiffness of tissue, or the anatomy of a three-dimensional region. 
     SUMMARY 
     According to one aspect of the present application, an ultrasound device comprises a phase-locked loop (PLL) comprising a digitally-controlled oscillator (DCO). The DCO comprises a plurality of current source unit cells with drain switch and a plurality of current source unit cells with source switch. 
     In some embodiments, the plurality of current source unit cells with drain switch have a first circuit topology, the plurality of current source unit cells with source switch have a second circuit topology, and the first and second circuit topologies are different. 
     In some embodiments, the PLL is configured to use a fast switching technique that allows the PLL to power down when the ultrasound device is not generating data and to power up within 1 microsecond from when the ultrasound device begins to generate data again 
     In some embodiments, switching on one of the plurality of current source unit cells with drain switch causes a voltage transition at an internal node of the current source unit cell with drain switch proceeding in a first voltage direction, switching on of the plurality of current source unit cells with source switch causes a voltage transition at an internal node of the current source unit cell with source switch proceeding in a second voltage direction, and the first and second voltage directions are opposite. 
     In some embodiments, each of the plurality of current source unit cells with drain switch comprises a switch and a current source. The current source comprises a first terminal and a second terminal; and the switch is coupled to the first terminal of the current source; and each of the plurality of current source unit cells with source switch comprises the switch; and the current source. The switch is coupled to the second terminal of the current source. 
     In some embodiments, the current source comprises a single transistor, the first terminal comprises a drain of the transistor, and the second terminal comprises a source of the transistor. 
     In some embodiments, the current source comprises a cascode current source that comprises multiple transistors, the first terminal comprises a drain of one of the multiple transistors, and the second terminal comprises a source of the one of the multiple transistors. 
     In some embodiments, the switch comprises a single transistor. 
     In some embodiments, the switch comprises a transmission gate. 
     In some embodiments, the current source comprises at least one transistor having a gate terminal, and the gate terminal is coupled to an output of a resistor-capacitor (RC) filter. 
     In some embodiments, the RC filter is coupled to an output terminal of bias generation circuitry. 
     In some embodiments, the switch comprises at least one transistor having a gate terminal; the PLL comprises a decoder having a plurality of output terminals; and the gate terminal of the transistor is coupled to one of the plurality of output terminals of the decoder. 
     In some embodiments, the DCO comprises a ring oscillator; and each of the plurality of current source unit cells with drain switch and each of the plurality of current source unit cells with source switch is couplable to the ring oscillator. 
     In some embodiments, the ring oscillator is configured to generate a clock signal having a frequency that depends on an amount of current that the ring oscillator receives from the plurality of current source unit cells with drain switch and the plurality of current source unit cells with source switch. 
     In some embodiments, the ultrasound device is configured to control the frequency of the clock signal, at least in part, by switching on a certain number of the plurality of current source unit cells with drain switch and a certain number of the plurality of current source unit cells with source switch. 
     In some embodiments, the ultrasound device further comprises control circuitry comprising coarse control circuitry configured to control how many blocks of one or more of the plurality of current source unit cells with drain switch and/or one or more of the plurality of current source unit cells with source switch are turned on. 
     In some embodiments, each of the plurality of current source unit cells with drain switch and each of the plurality of current source unit cells with source switch is coupled to an output terminal of a resistor-capacitor (RC) filter. A ratio between a decrease in voltage at the output terminal of the RC filter caused by one of the plurality of current source unit cell with drain switch switching on to an increase in voltage at the output terminal of the RC filter caused by one of the current source unit cell with source switch switching on is m:n. Each or approximately each of the blocks comprises 1+floor (n/m) current source unit cells with a composition of floor (n/m) current source unit cells with drain switch and one current source unit cell with source switch. 
     According to another aspect of the present application, a method, comprise using an ultrasound device comprising a phase-locked loop (PLL). The PPL comprises a digitally-controlled oscillator (DCO) comprising a plurality of current source unit cells with drain switch; and a plurality of current source unit cells with source switch. Using the ultrasound device comprises switching on a certain number of the plurality of current source unit cells with drain switch and a certain number of the plurality of current source unit cells with source switch. 
     In some embodiments, the plurality of current source unit cells with drain switch have a first circuit topology, the plurality of current source unit cells with source switch have a second circuit topology, and the first and second circuit topologies are different. 
     In some embodiments, the PLL is configured to use a fast switching technique that allows the PLL to power down when the ultrasound device is not generating data and to power up within 1 microsecond when the ultrasound device begins to generate data again. 
     In some embodiments, switching on one of the plurality of current source unit cells with drain switch causes a voltage transition at an internal node of the current source unit cell with drain switch proceeding in a first voltage direction, switching on of the plurality of current source unit cells with source switch causes a voltage transition at an internal node of the current source unit cell with source switch proceeding in a second voltage direction, and the first and second voltage directions are different. 
     In some embodiments, each of the plurality of current source unit cells with drain switch comprises a switch and a current source. The current source comprises a first terminal and a second terminal; and the switch is coupled to the first terminal of the current source; and 
     each of the plurality of current source unit cells with source switch comprises the switch and the current source. The switch is coupled to the second terminal of the current source. 
     In some embodiments, the current source comprises a single transistor, the first terminal comprises a drain of the transistor, and the second terminal comprises a source of the transistor. 
     In some embodiments, the current source comprises a cascode current source that comprises multiple transistors, the first terminal comprises a drain of one of the multiple transistors, and the second terminal comprises a source of the one of the multiple transistors. 
     In some embodiments, the switch comprises a single transistor. 
     In some embodiments, the switch comprises a transmission gate. 
     In some embodiments, the current source comprises at least one transistor having a gate terminal, and the gate terminal is coupled to an output of a resistor-capacitor (RC) filter. 
     In some embodiments, the RC filter is coupled to an output terminal of bias generation circuitry. 
     In some embodiments, the switch comprises at least one transistor having a gate terminal; the PLL comprises a decoder having a plurality of output terminals; and the gate terminal of the transistor is coupled to one of the plurality of output terminals of the decoder. 
     In some embodiments, the DCO comprises a ring oscillator; and each of the plurality of current source unit cells with drain switch and each of the plurality of current source unit cells with source switch is couplable to the ring oscillator. 
     In some embodiments, using the ultrasound device comprises using the ring oscillator is configured to generate a clock signal having a frequency that depends on an amount of current that the ring oscillator receives from the plurality of current source unit cells with drain switch and the plurality of current source unit cells with source switch 
     In some embodiments, using the ultrasound device comprises controlling the frequency of the clock signal, at least in part, by switching on the certain number of the plurality of current source unit cells with drain switch and the certain number of the plurality of current source unit cells with source switch. 
     In some embodiments, the ultrasound device further comprises control circuitry comprising coarse control circuitry. Using the ultrasound device comprises using the coarse control circuitry to switch on or off of blocks comprising one or more of the plurality of current source unit cells with drain switch and or more of the plurality of current source unit cells with source switch at a time. 
     In some embodiments, each of the plurality of current source unit cells with drain switch and each of the plurality of current source unit cells with source switch is coupled to an output terminal of a resistor-capacitor (RC) filter; the RC filter is coupled to an output terminal of bias generation circuitry; a ratio between a decrease in voltage at the output terminal of the RC filter caused by one of the plurality of current source unit cell with drain switch switching on to an increase in voltage at the output terminal of the RC filter caused by one of the current source unit cell with source switch  114   b  switching on is m:n; each or approximately each of the blocks comprises 1+floor (n/m) current source unit cells with a composition of floor (n/m) current source unit cells with drain switch and one current source unit cell with source switch. 
     According to another aspect of the present application, an ultrasound device comprises a plurality of ultrasound transducers, serializer-deserializer (SerDes) circuitry coupled to the plurality of ultrasound transducers, and a phase-locked loop (PLL) comprising a plurality of current source unit cells of a first type and a plurality of current source unit cells of a second type different from the first type. 
     In some embodiments, at least one of the plurality of current source unit cells of the first type is configured to produce a first voltage increase when turned on, and wherein at least one of the plurality of current source unit cells of the second type is configured to produce a first voltage decrease when turned on. 
     In some embodiments, the at least one of the plurality of current source unit cells of the first type is configured to produce a second voltage decrease when turned off, and wherein the at least one of the plurality of current source unit cells of the second type is configured to produce a second voltage increase when turned off. 
     In some embodiments, at least one of the plurality of current source unit cells of the first type comprises a drain switch and at least one of the plurality of current source unit cells of the second type comprises a source switch. 
     In some embodiments, the source switch comprises a transmission gate. 
     In some embodiments, the source switch comprises a cascode current source. 
     According to another aspect of the present application, a method for operating an ultrasound device comprises producing a plurality of electric signals using a plurality of ultrasound transducers and combining the plurality of electric signals using serializer-deserializer (SerDes) circuitry. The combining comprises timing the SerDes circuitry using a phase-locked loop (PLL) at least in part by turning on a plurality of current source unit cells of a first type and at least in part by turning on a plurality of current source unit cells of a second type different from the first type. 
     In some embodiments, turning on the plurality of current source unit cells of the first type and turning on the plurality of current source unit cells of the second type comprises determining how many current source unit cells of the first type and how many current source unit cells of the second type should be turned on to limit a voltage disturbance. 
     In some embodiments, determining how many current source unit cells of the first type and how many current source unit cells of the second type should be turned on to limit the voltage disturbance comprises identifying a plurality of entries of a look-up table, that, collectively, yield a voltage disturbance below a predefined threshold. 
     Some aspects of the present application include at least one non-transitory computer-readable storage medium storing processor-executable instructions that, when executed by at least one processor, cause the at least one processor to perform the above aspects and embodiments. Some aspects include an apparatus having a processing device configured to perform the above aspects and embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various aspects and embodiments will be described with reference to the following exemplary and non-limiting figures. It should be appreciated that the figures are not necessarily drawn to scale. Items appearing in multiple figures are indicated by the same or a similar reference number in all the figures in which they appear. 
         FIG. 1  illustrates a schematic block diagram of circuitry in an ultrasound device, in accordance with certain embodiments described herein. 
         FIGS. 2-6  are circuit diagrams illustrating various examples of current source unit cells, in accordance with certain embodiments described herein. 
         FIG. 7  illustrates another schematic block diagram of circuitry in an ultrasound device, in accordance with certain embodiments described herein. 
         FIGS. 8-13  are circuit diagrams illustrating additional examples of current source unit cells, in accordance with certain embodiments described herein. 
         FIG. 14  is a plot illustrating representative voltage disturbances corresponding to different data sets, in accordance with certain embodiments described herein. 
         FIG. 15  illustrates a schematic block diagram of an ultrasound device, in accordance with certain embodiments described herein. 
     
    
    
     DETAILED DESCRIPTION 
     In some embodiments, an ultrasound device may include phase-locked loop (PLL) circuitry configured to generate a high-speed clock signal. For example, a PLL may provide the high-speed clock signal to serializer-deserializer (SerDes) circuitry, and the SerDes circuitry may be configured to use the high-speed clock signal to serialize and deserialize data signals. The data signals may be generated and processed by ultrasound sensors and receive circuitry in the ultrasound device. 
     In some embodiments, the PLL may be configured to generate the clock signal such that the clock signal has a frequency that can be digitally controlled. In particular, in some embodiments, the frequency may depend on the amount of current that a circuit in the PLL, a ring oscillator, receives from current source unit cells. The PLL may be configured to turn on a specific number of these current source unit cells to control the amount of current received by the ring oscillator and thereby control, at least in part, the frequency of the output clock signal. 
     In some embodiments, the PLL may use fast switching techniques that allow the PLL to power down and conserve power when the ultrasound device is not generating data, and power up to full operation within an acceptably fast period of time (e.g., within 1 microsecond) when the ultrasound device begins to generate data again. The inventors have recognized that when a current source unit cell switches on and off using such a fast switching technique, the current source unit cell may experience a large voltage transition in an internal node that may couple to one or more other nodes in the circuitry of the ultrasound device. The combined effect of all voltage transitions at all the current source unit cells may couple to a node supplying a bias voltage to the PLL, and this large disturbance may cause an increase in the settling time of the voltage at the bias node. If the voltage at this node does not settle sufficiently quickly, then the frequency of the output clock signal from the PLL may not settle in an acceptably short time period. 
     The inventors have realized that using two types of current source unit cells with two different circuit topologies may help to reduce the disturbance caused by fast switching of the current source unit cells. The topologies may be such that switching on of one type of current source unit cell may cause a voltage transition that proceeds in one voltage direction (e.g., a voltage increase) while switching on of the other type of current source unit cell may cause a voltage transition that proceeds in the opposite voltage direction (e.g., a voltage decrease). Additionally, or alternatively, the topologies may be such that switching off of one type of current source unit cell may cause a voltage transition that proceeds in one voltage direction (e.g., a voltage increase) while switching off of the other type of current source unit cell may cause a voltage transition that proceeds in the opposite voltage direction (e.g., a voltage decrease). Thus, the voltage transitions of multiple current source unit cells of the two types may cancel each other out, or at least attenuate any attenuate the total voltage disturbance. The total disturbance that may couple to the bias voltage node may therefore be less than if all the current source unit cells were of a single type and all the voltage transitions proceeded in the same direction. 
     In some embodiments, the PLL may include circuitry configured to turn on current source unit cells in blocks of multiple current source unit cells. The inventors have recognized that selecting a specific number of current source unit cells of each type in each block, and selecting a specific order in which current source unit cells turn on or off, may help to reduce the disturbance at the bias voltage node across all options for how many current source unit cells are turned on. 
     In the below description, a particular reference name (e.g., V out , V bias , V int , etc.) may refer either to a node of a circuit and/or the particular voltage at that node. As referred to herein, two elements (e.g., terminals, circuits, etc.) being “coupled” together may mean that the two elements are directly coupled together or that another element (e.g., a voltage buffer) is coupled between the two elements. 
     Various aspects of the present disclosure may be used alone, in combination, or in a variety of arrangements not specifically described in the embodiments described in the foregoing and is therefore not limited in its application to the details and arrangement of components set forth in the foregoing description or illustrated in the drawings. For example, aspects described in one embodiment may be combined in any manner with aspects described in other embodiments. 
       FIG. 1  illustrates a schematic block diagram of circuitry in an ultrasound device, in accordance with certain embodiments described herein. The circuitry in the ultrasound device includes a phase-locked loop (PLL)  102 , bias generation circuitry  104 , a resistor-capacitor (RC) filter  106 , and control circuitry  108 . The PLL  102  includes a digitally-controlled oscillator (DCO)  110  and PLL controller  111 . The DCO  110  includes a ring oscillator  112 , current source unit cells  114 , and a decoder  122 . The current source unit cells  114  include current source unit cells with drain switch  114   a  and current source unit cells with source switch  114   b.  The PLL controller  111  includes coarse control circuitry  113  and fine control circuitry  115 . The RC filter  106  includes a resistor R, a capacitor C, and ground  120 . 
     In some embodiments, the PLL  102  may be configured to generate a high-speed clock signal. For example, the PLL  102  may provide the high-speed clock signal to serializer-deserializer (SerDes) circuitry (not illustrated), and the SerDes circuitry may be configured to use the high-speed clock signal to serialize and deserialize data signals. The data signals may be generated and processed by ultrasound sensors and receive circuitry in the ultrasound device. Generally, the PLL  102  includes the DCO  110 , which may be configured to generate a clock signal having a frequency that can be digitally controlled, the PLL controller  111 , as well as other circuitry (not illustrated). The DCO  110 , the PLL controller  111 , and the other circuitry in the PLL  102  may be arranged in a feedback loop (not illustrated) configured to force the output high-speed clock signal from the PLL  102  to have the same phase as an input signal to the PLL  102  (clk_ref as illustrated in  FIG. 1 ) and a frequency that depends on the input signal (e.g., a multiple of the frequency of the input signal clk_ref). 
     As described above, in some embodiments, the DCO  110  may be configured to generate a clock signal having a frequency that can be digitally controlled. In particular, in some embodiments, the ring oscillator  112  may be configured to generate a clock signal having a frequency that depends on the amount of current that the ring oscillator  112  receives from the current source unit cells  114 . The current source unit cells  114  are coupled to the power supply  130  (generating a voltage that will be referred to as V DD ) at one end and couplable to the ring oscillator  112  at the other end. In some embodiments, each of the current source unit cells  114  may be configured to be coupled or decoupled from the ring oscillator  112 . When coupled to the ring oscillator  112 , each of the current source unit cells  114  may be configured to draw a certain amount of current, I out , from the power supply  130  that supply current to the ring oscillator  112 . If the number of current source unit cells  114  coupled to the ring oscillator  112  is equal to k, then the total amount of current received by the ring oscillator  112  may be equal to, or approximately equal to or proportional to, or approximately proportional to k×I out . As described above, the total amount of current received by the ring oscillator  112  may control the frequency of the clock signal that is generated by the ring oscillator  112 , and thus the values of k and I out  may control the frequency of the clock signal that is generated by the ring oscillator  112 . 
     The bias generation circuitry  104  may be configured to output a bias voltage. The bias generation circuitry  104  may include circuitry configured to generate a bias voltage that is stable despite any changes that may arise in voltage and/or temperature. The control circuitry  108  may be configured to control the bias generation circuitry  104 , using one of more digital signals bias_control, to output a particular bias voltage. The output of the bias generation circuitry  104  is coupled to the RC filter  106 . The RC filter  106  may include a low-pass filter configured to reduce noise on the bias voltage received from the bias generation circuitry  104  and output a filtered bias voltage V bias . Each of the current source unit cells  114  may receive the filtered bias voltage V bias  from the output of the RC filter  106 , and the value of V bias  may determine the amount of current I out  that is outputted by each of the current source unit cells  114 . As described above, the value of I out  may control, in part, the frequency of the clock signal that is generated by the ring oscillator  112 . 
     The control circuitry  108  may be configured to control the PLL  102  to cause the DCO  110  to couple a specific number k of the current source unit cells  114  to the ring oscillator  112 . The control circuitry  108  is configured to output an input clock signal clk_ref having a particular reference frequency and to provide the input clock signal to the PLL controller  111  of the PLL  102 . PLL controller  111  may be configured to generate multi-bit digital control signals based on the frequency of clk_ref and output the control signals to the decoder  122  of the DCO  110 . As will be described further below, the PLL controller  111  may use its coarse control circuitry  113  and its fine control circuitry  115  to generate two multi-bit digital control signals based on the frequency of the clk_ref and output the control signals to the decoder  122 . In some embodiments, the coarse control circuitry  113  may include frequency detection circuitry and the fine control circuitry  115  may include phase detection circuitry. In some embodiments, coarse_control is modulated by frequency detection circuitry until the frequency detection circuitry finds the optimum frequency band. coarse_control may be fixed when the PLL  102  has completed the frequency locking procedure. In some embodiments, fine_control may be set to half the maximum code (though other values are also possible) when coarse_control is fixed, and then may be modulated by phase detection circuitry. In some embodiments, coarse_control and fine_control may encode information indicating the number k of current source unit cells  114  that should be turned on. In some embodiments, coarse_control may control how many blocks of multiple current source unit cells  114  are turned on, and fine_control may control how many additional current source unit cells  114  may be turned on or off with single current source unit cell resolution. Further description of the coarse control circuitry  113  and the fine control circuitry  115  may be found below. 
     The decoder  122  may be configured to receive coarse_control and fine_control as inputs and decode them into control signals sw 1 , sw 2 , sw 3  . . . sw N−2 , sw N−1 , sw N  and/or the inverses of these control signals  sw 1   ,  sw 2   ,  sw 3    . . .  sw N−2   ,  sw N−1   ,  sw N   . In some embodiments, these control signals may be single-bit control signals, and in other embodiments, may include more than one bit. The control signals may be provided as inputs to the current source until cells  114 . Each of the control signals sw 1 , sw 2 , sw 3  . . . sw N−2 , sw N−1 , sw N  and/or their inverses  sw 1   ,  sw 2   ,  sw 3    . . .  sw N−2   ,  sw N−1   ,  sw N     may be inputted to a particular one of the current source until cells  114  and may be configured to control whether that particular current source unit cell  114  is coupled to or decoupled from the ring oscillator  112 . A particular control signal sw n  may include a bit that is a digital high (e.g., 1) when configured to control a particular current source unit cells  114  to be coupled to the ring oscillator  112  and is a digital low (e.g., 0) when configured to control a particular current source unit cells  114  to be decoupled from the ring oscillator  112  (although the opposite logic may be used in some embodiments). It should be appreciated that, depending on the circuitry within the current source unit cells  114 , each of the current source unit cells  114  may receive as inputs a control signal sw n , its inverse  sw n   , or both. For example, if a control signal is inputted to the gate of an n-type metal-oxide-semiconductor (nMOS) of a particular current source unit cell  114  to control whether the particular current source unit cell  114  is coupled to or decoupled from the ring oscillator  112 , the current source unit cell  114  may receive sw n . If a control signal is inputted to the gate of a p-type metal-oxide-semiconductor (pMOS) of a particular current source unit cell  114  to control whether the particular current source unit cell  114  is coupled to or decoupled from the ring oscillator  112 , the current source unit cell  114  may receive  sw n   . If control signals are inputted to the gate of an nMOS and a pMOS of a particular current source unit cell  114  to control whether the particular current source unit cell  114  is coupled to or decoupled from the ring oscillator  112 , the current source unit cell  114  may receive both sw n  and  sw n   . 
     As a non-limiting example, consider that each of the current source unit cells  114  outputs current to the ring oscillator  112  when receiving a control signal sw n  that is digital high. For given values of coarse_control and fine_control, the decoder  122  may output control signals such that sw 1 , sw 2 , sw 3  . . . sw n  are digital high, thereby causing the current source until cells  114  receiving these control signals to output current to the ring oscillator  112 , and the decoder  122  may output control signals such that sw n+1 , sw n+2 , sw n+3  . . . sw N  are digital low, thereby causing the current source until cells  114  receiving these control signals to not output current to the ring oscillator  112 . In other words, the values coarse_control and fine_control may control k, namely how many current source until cells  114  are supplying current to the ring oscillator  112 . As described above, the value of k may determine, in part, the frequency of the clock signal that is generated by the ring oscillator  112 . Thus, because the control circuitry  108  may control k and I out , as described above, the control circuitry  108  may control the frequency of the clock signal that is generated by the ring oscillator  112 . 
     In some embodiments, the PLL  102  may use fast switching techniques. For example, the PLL  102  may include transceiver circuitry that allows the PLL  102  to power down and conserve power when the ultrasound device is not generating data, and power up to full operation within an acceptably fast period of time (e.g., within 1 microsecond) when the ultrasound device begins to generate data again. For further description of fast techniques, see Wei, Da, et al., “A 10-Gb/s/ch, 0.6-pJ/bit/mm Power Scalable Rapid-ON AND/OR OFF Transceiver for On-Chip Energy Proportional Interconnects,” I9 Journal of Solid-State Circuits 53.3 (2018): 873-883. When each of the current source unit cells  114  switches on and off using such a fast switching technique, the current source unit cells  114  may cause a large disturbance that may couple to the node V bias . In particular, when switching on or off, each of the current source unit cells  114  may experience a voltage transition (e.g., a voltage spike and the associated settling time) at an internal node that may couple to the node V bias . The combined effect of all voltage transitions at all the current source unit cells  114  coupling to the node V bias  may cause a large disturbance in the voltage at V bias . This large disturbance may cause an increase in the settling time of V bias . If the voltage V bias  does not settle fast, then the frequency of the output signal from the DCO  110  may not settle in an acceptably short time period. This may negatively affect the performance of the ultrasound device. For example, a frequency of the output signal from the DCO  110  not settling in an acceptably short time period may result in bit errors. Bit errors, in turn, may lead to blurry images or, in some instances, to image frame loss. 
     The inventors have realized that using two types of current source unit cells  114  may help to reduce the disturbance caused by fast switching of the current source unit cells  114 . In some embodiments, one type of current source unit cell includes a drain switch  114   a  and another type of current source unit cell includes a source switch  114   b,  although in other embodiments the types of current source unit cell may differ from one another in other respects. The current source unit cells with drain switch  114   a  may have a different circuit topology than the current source unit cells with source switch  114   b.  In particular, the topologies may be such that fast switching of the current source unit cells with drain switch  114   a  causes a voltage transition that proceeds in one voltage direction (e.g., the voltage increases) while fast switching of the current source unit cells with source switch  114   a  causes a voltage transition that proceeds in the opposite voltage direction (e.g., if the drain switch causes the voltage to increases, the source switch may cause the voltage to decrease, or vice versa). Thus, the voltage transitions of multiple current source unit cells  114  of the two types may cancel each other out to a certain degree. The total disturbance that may couple to the node V bias  may be therefore be less than if all the current source unit cells  114  were of a single type and all the voltage transitions proceeded in the same direction. 
     Consider the following non-limiting example. As illustrated in  FIG. 1 , the current source unit cells  114  are coupled to a power supply  130  generating a voltage that will be referred to as V DD . The voltage of the output nodes of the current source unit cells  114 , which are couplable to the ring oscillator  112 , will be referred to as V out . When the current source unit cells with drain switch  114   a  turn on, nodes internal to the current source unit cells with drain switch  114   a  may transition from V DD  to V out , and the transition at these nodes may couple to the node V bias . When the current source unit cells with source switch  114   b  turn on, nodes internal to the current source unit cells with source switch  114   b  may transition from V out  to V DD , and the transition at these nodes may couple to the node V bias . It should be appreciated that these two transitions proceed in opposite voltage directions and thus may cancel each other out to a certain degree. 
     It should be appreciated that, when turning on a certain number (e.g., k) of the current source unit cells  114  as described above, this may include turning a first number of the current source unit cells with drain switch  114   a  and a second number of the current source unit cells with source switch  114   b,  and the first and second numbers may be different in some embodiments. 
       FIG. 2  illustrates a circuit diagram of a current source unit cell with drain switch  214   a,  in accordance with certain embodiments described herein. In some embodiments, some or all of the current source unit cells with drain switch  114   a  in  FIG. 1  may have the topology of the current source unit cell with drain switch  214   a.  The current source unit cell with drain switch  214   a  includes a first p-type metal-oxide-semiconductor (pMOS) transistor  224  and a second pMOS transistor  226 . The first pMOS transistor  224  includes a gate terminal  224   g,  a drain terminal  224   d,  and a source terminal  224   s.  The second pMOS transistor  226  includes a gate terminal  226   g,  a drain terminal  226   d,  and a source terminal  226   s.  The gate terminal  224   g  of the first pMOS transistor  224  is coupled to the node V bias  (i.e., the output of the RC filter  106 ). The source terminal  224   s  of the first pMOS transistor  224  is coupled to the power supply  130 . The drain terminal  224   d  of the first pMOS transistor  224  is coupled to the source terminal  226   s  of the second pMOS transistor  226  at an internal node (referred to as V int,n ) not shared with other current source unit cells  114 . The gate terminal  226   g  of the second pMOS transistor  226  is coupled to a signal  sw n     (i.e., one of the outputs of the decoder  122 ). The drain terminal  226   d  of the second pMOS transistor  226  is couplable to the ring oscillator  112  at a node (referred to as V out ) that is shared by other current source unit cells  114 . The first pMOS transistor  224  functions as a current source, generating the current I out  having a value depending on the value of V bias . The second pMOS transistor  226  functions as a switch, enabling (when  sw n    is low) or disabling (when  sw n    is high) the flow of the current I out  from the first pMOS transistor  224  to the ring oscillator  112 . It should be appreciated that the current source unit cell with drain switch  214   a  is referred to as having a “drain switch” because the second pMOS transistor  226 , which functions as a switch, is coupled to the drain  224   d  of the first pMOS transistor  224 , which functions as a current source. 
     Refer to the voltage at the power supply  130  node as V DD , the voltage at the drain terminal  226   d  of the second pMOS transistor  226  which is couplable to the ring oscillator  112  as V out , and the voltage at the internal node to which the drain terminal  224   d  of the first pMOS transistor  224  and the source terminal  226   s  of the second pMOS transistor  226  are coupled as V int,n . When the second pMOS transistor  226   d,  which functions as a switch, turns on, the voltage V int,n  may transition from V DD  to V out . When the second pMOS transistor  226   d,  which functions as a switch, turns off, the voltage V int,n  may transition from V out  to V DD . 
       FIG. 3  illustrates a circuit diagram of a current source unit cell with source switch  314   b,  in accordance with certain embodiments described herein. In some embodiments, some or all of the current source unit cells with source switch  114   b  in  FIG. 1  may have the topology of the current source unit cell with source switch  314   b.  The current source unit cell with source switch  314   b  includes a first p-type metal-oxide-semiconductor (pMOS) transistor  324  and a second pMOS transistor  326 . The first pMOS transistor  324  includes a gate terminal  324   g,  a drain terminal  324   d,  and a source terminal  324   s.  The second pMOS transistor  326  includes a gate terminal  326   g,  a drain terminal  326   d,  and a source terminal  326   s.  The gate terminal  324   g  of the first pMOS transistor  324  is coupled to a signal  sw n     (i.e., one of the outputs of the decoder  122 ). The source terminal  324   s  of the first pMOS transistor  324  is coupled to the power supply  130 . The drain terminal  324   d  of the first pMOS transistor  324  is coupled to the source terminal  326   s  of the second pMOS transistor  326  at an internal node (referred to as V int,n ) not shared with other current source unit cells  114 . The gate terminal  326   g  of the second pMOS transistor  326  is coupled to the node V bias  (i.e., the output of the RC filter  106 ). The drain terminal  326   d  of the second pMOS transistor  326  is couplable to the ring oscillator  112  at a node (referred to as V out ) that is shared by other current source unit cells  114 . The second pMOS transistor  326  functions as a current source, generating the current I out  having a value depending on the value of V bias . The first pMOS transistor  324  functions as a switch, enabling (when  sw n     is low) or disabling (when  sw n     is high) the flow of the current I out  from the second pMOS transistor  326  to the ring oscillator  112 . It should be appreciated that the current source unit cell with source switch  314   b  is referred to as having a “source switch” because the first pMOS transistor  324 , which functions as a switch, is coupled to the source  324   s  of the second pMOS transistor  326 , which functions as a current source. 
     Refer to the voltage at the power supply  130  node as V DD , the voltage at the drain terminal  326   d  of the second pMOS transistor  326  which is couplable to the ring oscillator  112  as V out , and the voltage at the internal node to which the drain terminal  324   d  of the first pMOS transistor  324  and the source terminal  326   s  of the second pMOS transistor  326  are coupled as V int,n . When the second pMOS transistor  326   d,  which functions as a switch, turns on, the voltage V int,n  may transition from V out  to V DD . When the second pMOS transistor  226   d,  which functions as a switch, turns off, the voltage V int,n  may transition from V DD  to V out . 
       FIG. 4  illustrates a circuit diagram of a current source  434 , in accordance with certain embodiments described herein. The current source  434  may be considered to be a cascode current source. The current source  434  includes two pMOS transistors. The gate of one of the pMOS transistors is coupled to the node V bias . The gate of the other pMOS transistor is coupled to another bias voltage V bias,2 . The current source  434  may be used instead of a pMOS transistor functioning as a current source in any of the current source unit cells described above with reference to  FIGS. 2-3 . For example, a current source unit cell with drain switch may be formed by using the current source  434  instead of the first pMOS transistor  224  in the current source unit cell with drain switch  214   a.  As another example, a current source unit cell with source switch may be formed by using the current source  434  instead of the second pMOS transistor  326  in the current source unit cell with source switch  314   b.    
       FIG. 5  illustrates a circuit diagram of a current source  534 , in accordance with certain embodiments described herein. The current source  534  may be considered to be a double-cascode current source. The current source  534  includes three pMOS transistors. The gate of one of the pMOS transistors is coupled to the node V bias . The gates of the other two pMOS transistors are coupled to two other bias voltages, V bias,2  and V bias,3 , respectively. The current source  534  may be used instead of a pMOS transistor functioning as a current source in any of the current source unit cells described herein. For example, a current source unit cell with drain switch may be formed by using the current source  534  instead of the first pMOS transistor  224  in the current source unit cell with drain switch  214   a.  As another example, a current source unit cell with source switch may be formed by using the current source  534  instead of the second pMOS transistor  326  in the current source unit cell with source switch  314   b.    
       FIG. 6  illustrates a circuit diagram of a transmission gate  628 , in accordance with certain embodiments described herein. The transmission gate  628  includes a pMOS transistor  630  and an nMOS transistor  632 . The pMOS transistor  630  includes a gate terminal  630   g,  a drain terminal  630   d,  and a source terminal  630   s.  The nMOS transistor  632  includes a gate terminal  632   g,  a drain terminal  632   d,  and a source terminal  632   s.  The gate terminal  632   g  of the nMOS transistor  632  is coupled to a signal sw n  (i.e., one of the outputs of the decoder  122 ) and the gate terminal  630   g  of the pMOS transistor  630  is coupled to  sw n   , the inverse of the signal swn. The drain terminal  630   d  of the pMOS transistor  630  is coupled to the drain terminal  632   d  of the nMOS transistor  632 . The source terminal  630   s  of the pMOS transistor  630  is coupled to the source terminal  632   s  of the pMOS transistor  632 . 
     The transmission gate  628  may be used instead of a transistor functioning as a switch in any of the current source unit cells described with reference to  FIGS. 2-5 . For example, a current source unit cell with drain switch  114   a  may be formed by using the transmission gate  628  instead of the second pMOS transistor  226  in the current source unit cell with drain switch  214   a  (whether with or without substitution of the current source  434  or the current source  534  for the first pMOS transistor  224 ). As another example, a current source unit cell with source switch  114   b  may be formed by using the transmission gate  628  instead of the first pMOS transistor  324  in the current source unit cell with source switch  314   b  (whether with or without substitution of the current source  434  or the current source  534  for the second pMOS transistor  326 ). 
     Referring back to  FIG. 1 , the current source unit cells with drain switch  114   a  may have the topology of the current source unit cell with drain switch  214   a.  In some embodiments, the topology of the current source unit cell with drain switch  214   a  may be substituted with the current source  434 . In some embodiments, the topology of the current source unit cell with drain switch  214   a  may be substituted with the current source  534 . In some embodiments, the topology of the current source unit cell with drain switch  214   a  may be substituted with the transmission gate  628  In some embodiments, the topology of the current source unit cell with drain switch  214   a  may be substituted with the current source  434  and the transmission gate  628 , or the topology of the current source unit cell with drain switch  214   a  may substituted with the current source  534  and the transmission gate  628 . In some embodiments, all the current source unit cells with drain switch  114   a  have the same topology. Alternatively, some of the current source unit cells with drain switch  114   a  may have one of the topologies described above, others may have others of these topologies, etc. The current source unit cells with source switch  114   b  may have the topology of the current source unit cell with source switch  314   b.  In some embodiments, the topology of the current source unit cell with source switch  314   b  may be substituted with the current source  434 . In some embodiments, the topology of the current source unit cell with source switch  314   b  may be substituted with the current source  534 . In some embodiments, the topology of the current source unit cell with source switch  314   b  may be substituted with the transmission gate  628 . In some embodiments, the topology of the current source unit cell with source switch  314   b  may be substituted with the current source  434  and the transmission gate  628 , or the topology of the current source unit cell with source switch  314   b  may be substituted with the current source  534  and the transmission gate  628 . In some embodiments, all the current source unit cells with source switch  114   b  have the same topology. Alternatively, some of the current source unit cells with source switch  114   b  may have one of the topologies described above, others may have others of these topologies, etc. 
     It should be appreciated from the above description that, in any of the topologies for the current source unit cells with drain switch  114   a  described above, when the switch of the current source unit cell turns on to allow current to flow from the current source, the voltage of the internal node V int,n  may transition from V DD  to V out . When the switch of the current source unit cell turns off to prevent current from flowing from the current source, the voltage of the internal node V int,n  may transition from V out  to V DD  . By contrast, in any of the topologies for the current source unit cells with source switch  114   b  described above, when the switch of the current source unit cell turns on to allow current to flow from the current source, the voltage of the internal node V int,n  may transition from V out  to V DD  . When the switch of the current source unit cell turns off to prevent current from flowing from the current source, the voltage of the internal node V int,n  may transition from V DD  to V out . Thus, the voltage transition at the internal node V int,n  when switching on may proceed in the opposite direction for current source unit cells with drain switch compared with that with source switch, and the voltage transition at the internal node V int,n  when switching on may proceed in the opposite direction for current source unit cells with drain switch compared with that with source switch, Thus, if one or more current source unit cells with drain switch and one or more current source unit cells with source switch on or off together, the voltage transitions at the internal nodes V int,n  of each of the current source unit cells of the first and second types may proceed in opposite voltage directions and may cancel each other out to a certain degree. The total disturbance that may couple to the node V bias  from the internal nodes V int,n  may therefore be less than if all the current source unit cells were of a single type and all the voltage transitions proceeded in the same direction. 
       FIG. 7  illustrates a schematic block diagram of circuitry in an ultrasound device, in accordance with certain embodiments described herein. The circuitry in  FIG. 7  is is similar in some respects to the circuitry in  FIG. 1  except that the circuitry in  FIG. 7  includes the PLL  702 , which includes the DCO  710 , instead of the PLL  102  and the DCO  110 . The DCO  710  includes current source unit cells  714 , which include current source unit cells with drain switch  714   a  and current source unit cells with source switch  714   b.  The current source unit cells  714  are coupled to ground  120  at one end and couplable to the ring oscillator  112  at the other end. In some embodiments, each of the current source unit cells  714  may be configured to be coupled or decoupled from the ring oscillator  112 . In contrast to the current source unit cells  114 , when coupled to the ring oscillator  112 , each of the current source unit cells  114  may be configured to sink a certain amount of current, I out , from the ring oscillator  114  and supply that current to ground  120 . 
       FIG. 8  illustrates a circuit diagram of a current source unit cell with drain switch  814   a,  in accordance with certain embodiments described herein. In some embodiments, some or all of the current source unit cells with drain switch  714   a  in  FIG. 7  may have the topology of the current source unit cell with drain switch  814   a.  The current source unit cell with drain switch  814   a  includes a first n-type metal-oxide-semiconductor (nMOS) transistor  824  and a second nMOS transistor  826 . The first nMOS transistor  824  includes a gate terminal  824   g,  a drain terminal  824   d,  and a source terminal  824   s.  The second nMOS transistor  826  includes a gate terminal  826   g,  a drain terminal  826   d,  and a source terminal  826   s.  The gate terminal  824   g  of the first nMOS transistor  824  is coupled to a signal sw n  (i.e., one of the outputs of the decoder  122 ). The drain terminal  824   d  of the first nMOS transistor  824  is couplable to the ring oscillator  112  at a node (referred to as V out ) that is shared by other current source unit cells  114 . The source terminal  824   s  of the first nMOS transistor  824  is coupled to the drain terminal  826   d  of the second nMOS transistor  826  at an internal node (referred to as V int,n ) not shared with other current source unit cells  714 . The gate terminal  826   g  of the second nMOS transistor  826  is coupled to a signal the node V bias  (i.e., the output of the RC filter  106 ). The source terminal  826   s  of the second nMOS transistor  826  is coupled to ground  120 . The second nMOS transistor  826  functions as a current source, generating the current I out  having a value depending on the value of V bias . The first nMOS transistor  824  functions as a switch, enabling (when sw n  is high) or disabling (when sw n  is low) the flow of the current I out  from the second nMOS transistor  826  to the ring oscillator  112 . It should be appreciated that the current source unit cell with drain switch  814   a  is referred to as having a “drain switch” because the first nMOS transistor  824 , which functions as a switch, is coupled to the drain  824   d  of the second nMOS transistor  826 , which functions as a current source. 
     Refer to the voltage at ground  120  as gnd, the voltage at the source terminal  826   s  of the second nMOS transistor  826  which is couplable to the ring oscillator  112  as V out , and the voltage at the internal node to which the source terminal  824   s  of the first nMOS transistor  824  and the drain terminal  826   d  of the second nMOS transistor  826  are coupled as V int,n . When the first nMOS transistor  824 , which functions as a switch, turns on, the voltage V int,n  may transition from gnd to V out . When the first nMOS transistor  824 , which functions as a switch, turns off, the voltage V int,n  may transition from V out  to gnd. 
       FIG. 9  illustrates a circuit diagram of a current source unit cell with source switch  914   b,  in accordance with certain embodiments described herein. In some embodiments, some or all of the current source unit cells with source switch  714   b  in  FIG. 7  may have the topology of the current source unit cell with source switch  914   b.  The current source unit cell with source switch  914   b  includes a first n-type metal-oxide-semiconductor (nMOS) transistor  924  and a second nMOS transistor  926 . The first nMOS transistor  924  includes a gate terminal  924   g,  a drain terminal  924   d,  and a source terminal  924   s.  The second nMOS transistor  926  includes a gate terminal  926   g,  a drain terminal  926   d,  and a source terminal  926   s.  The gate terminal  924   g  of the first nMOS transistor  924  is coupled to the node V bias  (i.e., the output of the RC filter  106 ). The drain terminal  924   d  of the first nMOS transistor  924  is couplable to the ring oscillator  112  at a node (referred to as V out ) that is shared by other current source unit cells  114 . The source terminal  924   s  of the first nMOS transistor  924  is coupled to the drain terminal  926   d  of the second nMOS transistor  926  at an internal node (referred to as V int,n ) not shared with other current source unit cells  714 . The gate terminal  926   g  of the second nMOS transistor  926  is coupled to a signal sw n  (i.e., one of the outputs of the decoder  122 ). The source terminal  926   s  of the second nMOS transistor  926  is coupled to ground  120 . The first nMOS transistor  924  functions as a current source, generating the current I out  having a value depending on the value of V bias . The second nMOS transistor  926  functions as a switch, enabling (when sw n  is high) or disabling (when sw n  is low) the flow of the current I out  from the first nMOS transistor  924  to the ring oscillator  112 . It should be appreciated that the current source unit cell with source switch  914   b  is referred to as having a “source switch” because the second nMOS transistor  926 , which functions as a switch, is coupled to the source  924   s  of the first nMOS transistor  924 , which functions as a current source. 
     Refer to the voltage at ground  120  as gnd, the voltage at the source terminal  926   s  of the second nMOS transistor  926  which is couplable to the ring oscillator  112  as V out , and the voltage at the internal node to which the source terminal  924   s  of the first nMOS transistor  924  and the drain terminal  926   d  of the second nMOS transistor  926  are coupled as V int,n . When the second nMOS transistor  926 , which functions as a switch, turns on, the voltage V int,n  may transition from V out  to gnd. When the second nMOS transistor  926   d,  which functions as a switch, turns off, the voltage V int,n  may transition from gnd to V out . 
       FIG. 10  illustrates a circuit diagram of a current source  1034 , in accordance with certain embodiments described herein. The current source  1034  may be considered to be a cascode current source. The current source  1034  includes two nMOS transistors. The gate of one of the nMOS transistors is coupled to the node V bias . The gate of the other nMOS transistor is coupled to another bias voltage V bias,2 . The current source  1034  may be used instead of a nMOS transistor functioning as a current source in any of the current source unit cells described herein. For example, a current source unit cell with source switch may be formed by using the current source  1034  instead of the second pMOS transistor  826  in the current source unit cell with source switch  814   a  (whether with or without substitution of the transmission gate  628 ). As another example, a current source unit cell with drain switch may be formed by using the current source  1034  instead of the first nMOS transistor  924  in the current source unit cell with drain switch  914   b  (whether with or without substitution of the transmission gate  628 ). 
       FIG. 11  illustrates a circuit diagram of a current source  1134 , in accordance with certain embodiments described herein. The current source  1134  may be considered to be a double-cascode current source. The current source  1134  includes three nMOS transistors. The gate of one of the nMOS transistors is coupled to the node V bias . The gates of the other two nMOS transistors are coupled to two other bias voltages, V bias,2  and V bias,3 , respectively. The current source  1134  may be used instead of a nMOS transistor functioning as a current source in any of the current source unit cells described herein. For example, a current source unit cell with source switch may be formed by using the current source  1134  instead of the second pMOS transistor  826  in the current source unit cell with source switch  814   a.  As another example, a current source unit cell with drain switch may be formed by using the current source  1134  instead of the first nMOS transistor  924  in the current source unit cell with drain switch  914   b.    
     Referring back to  FIG. 6 , the transmission gate  628  may be used instead of a transistor functioning as a switch in any of the current source unit cells described with reference to  FIGS. 8-11 . For example, a current source unit cell with drain switch  714   a  may be formed by using the transmission gate  628  instead of the first nMOS transistor  824  in the current source unit cell with source switch  814   a  (whether with or without substitution of the current source  1034  or the current source  1134  for the first nMOS transistor  824 ). As another example, a current source unit cell with drain switch may be formed by using the transmission gate  628  instead of the second nMOS transistor  926  in the current source unit cell with drain switch  914   b  (whether with or without substitution of the current source  1034  or the current source  1134  for the second nMOS transistor  926 ). 
     Referring back to  FIG. 7 , the current source unit cells with drain switch  714   a  may have the topology of the current source unit cell with drain switch  814   a,  the topology of the current source unit cell with drain switch  814   a  being substituted with the current source  1034 . In some embodiments, the topology of the current source unit cell with drain switch  814   a  may be substituted with the current source  1134 . In some embodiments, the topology of the current source unit cell with drain switch  814   a  may be substituted with the transmission gate  628 . In some embodiments, the topology of the current source unit cell with drain switch  814   a  may be substituted with the current source  1034  and the transmission gate  628 , or the topology of the current source unit cell with drain switch  814   a  may be substituted with the current source  1134  and the transmission gate  628 . In some embodiments, all the current source unit cells with drain switch  714   a  have the same topology. Alternatively, some of the current source unit cells with drain switch  714   a  may have one of the topologies described above, others may have others of these topologies, etc. The current source unit cells with source switch  714   b  may have the topology of the current source unit cell with source switch  914   b.  In some embodiments, the topology of the current source unit cell with source switch  914   b  may be substituted with the current source  1034 . In some embodiments, the topology of the current source unit cell with source switch  914   b  may be substituted with the current source  1134 . In some embodiments, the topology of the current source unit cell with source switch  914   b  may be substituted with the transmission gate  628 . In some embodiments, the topology of the current source unit cell with source switch  914   b  may be substituted with the current source  1134  and the transmission gate  628 , or the topology of the current source unit cell with source switch  914   b  may be substituted with the current source  1134  and the transmission gate  628 . In some embodiments, all the current source unit cells with source switch  714   b  have the same topology. Alternatively, some of the current source unit cells with source switch  714   b  may have one of the topologies described above, others may have others of these topologies, etc. 
     It should be appreciated from the above description that, in any of the topologies for the current source unit cells with drain switch  714   a  described above, when the switch of the current source unit cell turns on to allow current to flow from the current source, the voltage of the internal node V int,n  may transition from gnd to V out . When the switch of the current source unit cell turns off to prevent current from flowing from the current source, the voltage of the internal node V int,n  may transition from V out  to gnd. By contrast, in any of the topologies for the current source unit cells with source switch  714   b  described above, when the switch of the current source unit cell turns on to allow current to flow from the current source, the voltage of the internal node V int,n  may transition from V out  to gnd. When the switch of the current source unit cell turns off to prevent current from flowing from the current source, the voltage of the internal node V int,n  may transition from gnd to V out . Thus, the voltage transition at the internal node V int,n  when switching on may proceed in the opposite direction for current source unit cells with drain switch compared with that with source switch, and the voltage transition at the internal node V int,n  when switching on may proceed in the opposite direction for current source unit cells with drain switch compared with that with source switch, Thus, if one or more current source unit cells with drain switch and one or more current source unit cells with source switch on or off together, the voltage transitions at the internal nodes V int,n  of each of the current source unit cells of the first and second types may proceed in opposite voltage directions and may cancel each other out to a certain degree. The total disturbance that may couple to the node V bias  from the internal nodes V int,n  may be therefore be less than if all the current source unit cells were of a single type and all the voltage transitions proceeded in the same direction. 
     While the above description describes various example topologies of current source unit cells with drain switch and current source unit cells with source switch, these topologies are non-limiting. Generally, a current source unit cell with drain switch or the second type may be formed from a switch and a current source. The switch may be controlled by a signal sw n  (i.e., one of the outputs of the decoder  122 ) or its inverse  sw n   . For example, the switch may be a single transistor or a transmission gate. The current source may include at least one transistor having a gate coupled to V bias , and have two terminals. A current source unit cell with drain switch may be formed by coupling the switch to one terminal of the current source, and a current source unit cell with source switch may be formed by coupling the switch to the other terminal of the current source. In some embodiments, the current source may be a single transistor, and the current source unit cell with drain switch may have a switch coupled to the drain terminal of the single transistor, and the current source unit cell with source switch may have a switch coupled to the source terminal of the single transistor. In some embodiments, the current source may be a cascode current source including multiple transistors, and the current source unit cell with drain switch may have a switch coupled to the drain terminal of one of the transistors, and the current source unit cell with source switch may have a switch coupled to the source terminal of one of the transistors. 
     More generally, a current source unit cell with drain switch may have one circuit topology and a current source unit cell with source switch may have a different circuit topology, such that when the current source unit cell with drain switch switches on to allow current to flow, the voltage transition at one of its internal nodes proceeds in an opposite voltage direction than when the current source unit cell with source switch switches on to allow current flow, and when the current source unit cell with drain switch switches off to prevent current from flowing, the voltage transition at one of its internal nodes proceeds in an opposite voltage direction than when the current source unit cell with source switch switches off to prevent current from flowing. 
     Described above are examples of current source unit cells implemented using MOS transistors. However, not all embodiments are limited to these particular types of transistors. Other transistors may be used additionally or alternatively, including for example bipolar junction transistors (BJTs) and junction field effect transistors (JFETs), among other examples. For example, in the implementations described above, pMOS transistors may be replaced by p-n-p BJTs and nMOS transistors may be replaced by n-p-n BJTs. Accordingly, as used herein, the term “gate” may be used to identify either the gate of a field effect transistor or the base of a bipolar transistor; the term “drain” may be used to identify either the drain of a field effect transistor or the collector of a bipolar transistor; and the term “source” may be used to identify either the source of a field effect transistor or the emitter of a bipolar transistor. 
     The following description will analyze the voltage disturbance that may occur in the examples of the current source unit cell with drain switch  214   a  and the current source unit cell with source switch  314   b,  as well as optimization of patterns for turning on and off these example current source unit cells. Similar analysis may be used for any other current source unit cells described herein. 
       FIG. 12  illustrates the current source unit cell with drain switch  214   a  with the addition of a parasitic capacitance, in accordance with certain embodiments described herein. In particular,  FIG. 12  illustrates a parasitic capacitance Cgd between the gate  224   g  and the drain  224   d  of the first pMOS transistor  224 .  FIG. 12  further illustrates a small-signal equivalent for the RC filter  106  in which V bias  is assumed to be an AC ground, such that the resistor R and the capacitor C are in parallel to each other. The combined impedance ZL of the RC filter  106  may then be (R∥(1/sC)), where s represents a complex frequency parameter. In some embodiments, C may be large compared to R, such that ZL is approximately equal to 0. 
     V int,n  may couple to V bias  through Cgd. In particular, 
     
       
         
           
             
               V 
               bias 
             
             = 
             
               
                 
                   Z 
                   L 
                 
                 
                   
                     Z 
                     L 
                   
                   + 
                   
                     1 
                     
                       sC 
                       gd 
                     
                   
                 
               
               ⁢ 
               
                 
                   V 
                   int 
                 
                 . 
               
             
           
         
       
     
     Assume sC gd Z L &lt;&lt;1, then V bias =sC gd Z L V int . 
     V int,n  may couple to V bias  through Cgd. In particular, 
     
       
         
           
             
               V 
               bias 
             
             = 
             
               
                 
                   Z 
                   L 
                 
                 
                   
                     Z 
                     L 
                   
                   + 
                   
                     1 
                     
                       sC 
                       gd 
                     
                   
                 
               
               ⁢ 
               
                 
                   V 
                   int 
                 
                 . 
               
             
           
         
       
     
     Assume sC gd Z L &lt;&lt;, then V bias =sC gd Z L V int . Assume as a particular example that Cgd=2.1 fF and the voltage at V int,n  decreases by 196 mV when the current source unit cell with drain switch  214   a  turns on (e.g., the second pMOS transistor  226 , functioning as a switch, begins to allow current to flow from the first pMOS transistor  224 , functioning as a current source). (This value may be calculated using simulation.) Then, based on the above equation, the voltage at V bias  may decrease by 411.6×10 −15 ×sZL mV due to the turning on of one current source until cell with drain switch  214   a.    
       FIG. 13  illustrates the current source unit cell with source switch  314   b  with the addition of parasitic capacitances, in accordance with certain embodiments described herein. In particular,  FIG. 13  illustrates a parasitic capacitance Cgd between the gate  326   g  and the drain  326   d  of the second pMOS transistor  326  and a parasitic capacitance Cgs between the gate  326   g  and the source  326   s  of the second pMOS transistor  326 .  FIG. 13  further illustrates the small-signal equivalent for the RC filter  106  described in more detail above with reference to  FIG. 12 . 
     V int,n  and V out  may couple to V bias  through Cgs and Cgd, respectively. In particular, 
     
       
         
           
             
               V 
               bias 
             
             = 
             
               
                 
                   
                     Z 
                     L 
                   
                   
                     
                       Z 
                       L 
                     
                     + 
                     
                       1 
                       
                         sC 
                         gd 
                       
                     
                   
                 
                 ⁢ 
                 
                   V 
                   int 
                 
               
               + 
               
                 
                   
                     Z 
                     L 
                   
                   
                     
                       Z 
                       L 
                     
                     + 
                     
                       1 
                       
                         sC 
                         gd 
                       
                     
                   
                 
                 ⁢ 
                 
                   
                     V 
                     IOUT 
                   
                   . 
                 
               
             
           
         
       
     
     Assume sC gd Z L &lt;&lt;1 and sC gs Z L &lt;&lt;1, then V bias =sC gs Z L V int +sC gd Z L V IOUT . Assume as a particular example that Cgd=2.0 fF, Cgs=0.65 fF, the voltage at V int,n  increases by 348 mV when the current source unit cell with source switch  314   b  turns on (e.g., the first pMOS transistor  324 , functioning as a switch, begins to allow current to flow from the second pMOS transistor  326 , functioning as a current source), and the voltage at V out  increases by 514 mV when the current source unit cell with source switch  314   b  turns on. (This value may be calculated using simulation.) Then, based on the above equation, the voltage at V bias  may increase by 1254.2×10 −15 ×sZL mV due to the turning on of one current source until cell with drain switch  214   a.    
     It should thus be appreciated that in the example above, the current source unit cell  314   b,  when turning on, causes an increase in voltage at V bias  that is approximately 3 times as large as the decrease in voltage at V bias  caused by the current source unit cell  214   a  turning on. In other words, in this example, the ratio between the decrease in voltage at V bias  caused by the current source unit cell with drain switch  214   a  turning on to the increase in voltage at V bias  caused by the current source unit cell with source switch  314   b  turning on is approximately 1:3. Generally, the ratio between the decrease in voltage at V bias  caused by the current source unit cell with drain switch  214   a  turning on to the increase in voltage at V bias  caused by the current source unit cell with source switch  314   b  turning on may be C gd V int,D :C gs V int,S +C gd V out,S . In this equation, V int,D  is the decrease in voltage at V int,n  in the current source unit cell with drain switch  214   a  due the current source unit cell with drain switch  214   a  turning on, V int,S  is the increase in voltage at V int,n  in the current source unit cell with source switch  314   b  due the current source unit cell with source switch  314   b  turning on, and V out,S  is the increase in voltage at V out  in the current source unit cell with source switch  314   b  due the current source unit cell with source switch  314   b  turning on. 
     As described above, the current source unit cell with drain switch  214   a  turning on may cause a decrease in voltage at V bias  while the current source unit cell with source switch  314   b  turning on may cause an increase in voltage at V bias . However, other current source unit cells with drain switch, such as the current source unit cell with drain switch  814   a,  may cause an increase in voltage at V bias , and other current source unit cells with source switch, such as the current source unit cell with source switch  914   b,  may cause a decrease in voltage at V bias . While the above description has focused on deriving equations for the change in voltage at V bias  caused by the current source unit cell with drain switch  214   a  and the current source unit cell with source switch  314   b  turning on, similar circuit analysis may be used to derive equations for the change in voltage at V bias  caused by other current source unit cells with different circuit topologies. 
     Referring back to  FIG. 1  and as described above, the PLL controller  111  may control the DCO  110  to turn on the current source unit cells  114  using coarse control circuitry  113  and fine control circuitry  115 . Using the coarse control circuitry  113  may include controlling the DCO  110  to turn on or off blocks of multiple current source unit cells  114  at a time. Using the fine control circuitry  115  may include controlling the DCO  110  to turn on or off single current source unit cells  114  at a time. Implementing both coarse control circuitry  113  and fine control circuitry  115  may reduce the complexity and size of circuitry needed in the control circuitry  108 . 
     As a particular example, if a block includes four current source unit cells  114 , the control circuitry  108  may use the coarse control circuitry  113  to control the DCO  110  to turn on eight blocks of current source unit cells  114  and use the fine control circuitry  115  to control the DCO  110  to turn on one additional current source unit cell  114  for a total of 33 current source unit cells  114  turned on. As another example, the control circuitry  108  may use the coarse control circuitry  113  to control the DCO  110  to turn on eight blocks of current source unit cells  114  and use the fine control circuitry  115  to control the DCO  110  to turn off one current source unit cell  114  for a total of 31 current source unit cells  114  turned on. 
     Consider further that, in some embodiments, the current source unit cells  114  may be ordered in a particular order, such that each current source unit cell  114  can be associated with a number 1 . . . N, where there are N total current source unit cells  114 . In some embodiments, the control circuitry  108  may use the coarse control circuitry  113  and the fine control circuitry  115  such that only consecutively numbered current source unit cells  114  starting from position 1 may be turned on simultaneously. In other words, if k current source unit cells  114  are turned on, then those cells are numbered 1−k. As a particular example, if a block includes four current source unit cells  114 , the control circuitry  108  may use the coarse control circuitry  113  to control the DCO  110  to turn on eight blocks of current source unit cells  114  and use the fine control circuitry  115  to control the DCO  110  to turn off one current source unit cell  114  such that current source unit cells  114  numbered 1-31 are turned on. As another example, the control circuitry  108  may use the coarse control circuitry  113  to control the DCO  110  to turn on eight blocks of current source unit cells and use the fine control circuitry  115  to control the DCO  110  to turn on one additional current source unit cell  114  such that current source unit cells  114  numbered 1-33 are turned on. 
     Turning on a current source unit cell with drain switch  114   a  having a particular topology may cause a change in voltage at V bias  having a certain amplitude and polarity and turning on a current source unit cell with source switch  114   b  having a particular topology may cause a change in voltage at V bias  having a certain amplitude and polarity. For example, the current source unit cell  214   a  may cause a decrease in voltage at V bias  and the current source unit cell  314   b  may cause an increase in voltage at V bias , and the amplitude of the decrease in voltage may be less than the amplitude of the increase in voltage. However, in some embodiments, turning on a current source unit cell with drain switch  114   a  having a particular topology may cause an increase in voltage at V bias  and turning on a current source unit cell with source switch  114   b  having a particular topology may cause a decrease in voltage at V bias . Additionally or alternatively, turning on a current source unit cell with drain switch  114   a  having a particular topology may cause a change in voltage at V bias  having a larger amplitude than the amplitude of the change in voltage caused by turning on a current source unit cell with source switch  114   b  having a particular topology. 
     The total voltage disturbance at V bias  caused by all the current source unit cells turning on at a particular time may depend on how many current source unit cells with drain switch  114   a  and how many current source unit cells with source switch  114   b  are turned on simultaneously, as well as the value of the decrease in voltage at V bias  caused by a current source unit cell with drain switch  114   a  turning on and the value of the increase in voltage at V bias  caused by a current source unit cell with source switch  114   b  turning on. It may be helpful if, across all the options of how many current source unit cells  114  are turned on, the total voltage disturbance at V bias  is, on average, as close to 0 as possible. In other words, if there are N current source unit cells  114 , one may calculate the total voltage disturbance at V bias  when the current source unit cell  114  numbered 1 is turned on, when the current source unit cells  114  numbered 1-2 are turned on, when the current source unit cells  114  numbered 1-3 are turned on, etc. It may be helpful if the average of all the calculated total voltage disturbances is as close to 0 as possible. 
     The inventors have recognized that selecting a specific number of current source unit cells with drain switch  114   a  and the number of current source unit cells with source switch  114   b  in each block (i.e., a block in which all the current source unit cells are turned on or off with the coarse control circuitry  113 ), and selecting a specific ordering of the current source unit cells  114 , may help to reduce the disturbance at V bias  across all options for how many current source unit cells  114  are turned on. Consider that the ratio between the decrease in voltage at V bias  caused by the current source unit cell with drain switch  114   a  turning on to the increase in voltage at V bias caused by the current source unit cell with source switch  114   b  turning on is m:n. Then, using a size of 1+floor (n/m) current source unit cells  114  for each, (or approximately each) block and a block composition of floor (n/m) current source unit cells with drain switch  114   a  and 1 current source unit cell with source switch  114   b  may further help to reduce the disturbance at the V bias  node. 
     Table 1 illustrates two example block sizes and compositions for current source unit cells  114  where the decrease in voltage at V bias  caused by the current source unit cell with drain switch  114   a  turning on (m) is −4.87 mV and the increase in voltage at V bias  caused by the current source unit cell with source switch  114   b  turning on is 15.21 mV (n), such that the ratio m:n is 1:3.13. Case 2 of Table 1 illustrates an ordering of current source unit cells  114  using the above-described block size of 1+floor (n/m)=4 current source unit cells  114  and a block composition of floor (n/m)=3 current source unit cells with drain switch  114   a  and 1 current source unit cell with source switch  114   b.  Case 1 illustrates a different ordering that does not use the above-described block size or composition, but instead has a block size of 32 and a block composition of 24 current source unit cells with drain switch  114   a  and 8 current source unit cell with source switch  114   b.  Each row lists, in one column, whether the current source unit  114  at a particular position n in the order is a current source unit cell with drain switch  114   a  (“D”) or current source unit cell with source switch  114   b  (“S”). As can be seen, the ordering in Case 1 and Case 2 both include, in each block, all the current source unit cells with drain switch  114   a  (“D”) positioned first followed by all the current source unit cells with source switch  114   b  (“S”). Each row lists in the other column the sum of the voltage disturbances (in mV) caused at V bias  by the current source units  114  numbered 1−k when turned on. In other words, if the current source unit cells  114  numbered 1−k include d current source unit cells with drain switch  114   a  each contributing −4.87 mV to V bias  and s current source unit cells with source switch  114   b  each contributing 15.21 mV to V bias , then the total at each row may be 15.21 s-4.87 d. Generally, if the current source unit cells  114  numbered 1−k include d current source unit cells with drain switch  114   a  each contributing m to V bias  and s current source unit cells with source switch  114   b  each contributing n to V bias  then the total at each row may be ns−md. 
     When using a block composition of floor (n/m) current source unit cells with drain switch  114   a  and 1 current source unit cell with source switch  114   b,  there may be an error of (n/m−floor (n/m)). In the example above, the ratio m:n is 1:3.13. The block composition of 3 current source unit cells with drain switch  114   a  and 1 current source unit cells with source switch  114   b  may not account for the extra 0.13. In some embodiments, to compensate for this error, a current source unit cell with drain switch  114   a  may be added approximately every round ((1+floor (n/m))/(n/m−floor (n/m)) positions in the order. For example, in the above example, a current source unit cell with drain switch  114   a  may be added approximately every round (4/0.13)=30.77 positions in the order, or in practice, alternating every 31 st  and 30 th  positions in the order. Case 3 of Table 1 illustrates an ordering of current source unit cells  114  that is the same as Case 2, except that Case 3 includes an extra current source unit cell with drain switch  114   a  (“D”) added every 31 st  or 30 th  positions (alternating). The extra current source unit cell with drain switch  114   a  is illustrated with a bold “D”. 
     The total voltage disturbance may be further improved if the current source unit cell with source switch  114   b  (“S”) in each block is approximately in the middle of the block. For example, Case 4 illustrates an ordering that is the same as Case 3 but offset by 2 positions (in other words, starting from position 3 of Case 3) such that, in each block of size 4, the current source unit cell with source switch  114   b  (“S”) is at the second position rather than the last position (as it is in Case 3). 
     In general, Case 1 may be an ordering that has been optimized according to any of the criteria described above. Case 2 may be an ordering using a block size of 1+floor (n/m) and a block composition of floor (n/m)=current source unit cells with drain switch  114   a  and 1 current source unit cell with source switch  114   b.  Case 3 may be the same as Case 2 but with a current source unit cell with drain switch  114   a  added approximately every round ((1+floor (n/m))/(n/m−floor (n/m)) positions in the order. Case 4 may be the same as Case 3 but offset such that the current source unit cell with source switch  114   b  in each block is positioned approximately in the middle of each block. 
     In some embodiments, an ultrasound device may be hard coded based on the values of table 1. In other embodiments, table 1 may be stored as a look-up table in a memory of an ultrasound device (or a memory outside the ultrasound device). In some embodiments, determining how many current sources of type “D” (e.g., with drain switches) and how many current sources of type “S” (e.g., with source switches) should be turned on may involve identifying a plurality of entries (e.g., a pair of entries) of the look-up table, that, collectively, yield a voltage disturbance below a certain threshold. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Four different orderings of current source unit cells 114 and 
               
               
                 the total voltage disturbance caused to V bias  as a function 
               
               
                 of how many current source unit cells 114 are turned on. 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 # of Cells 
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 Turned On 
                 Case 1 
                   
                 Case 2 
                   
                 Case 3 
                   
                 Case 4 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 1 
                 D 
                 −4.87 
                 D 
                 −4.87 
                 D 
                 −4.87 
                 D 
                 −4.87 
               
               
                 2 
                 D 
                 −9.74 
                 D 
                 −9.74 
                 D 
                 −9.74 
                 S 
                 10.34 
               
               
                 3 
                 D 
                 −14.61 
                 D 
                 −14.61 
                 D 
                 −14.61 
                 D 
                 5.47 
               
               
                 4 
                 D 
                 −19.48 
                 S 
                 0.6 
                 S 
                 0.6 
                 D 
                 0.6 
               
               
                 5 
                 D 
                 −24.35 
                 D 
                 −4.27 
                 D 
                 −4.27 
                 D 
                 −4.27 
               
               
                 6 
                 D 
                 −29.22 
                 D 
                 −9.14 
                 D 
                 −9.14 
                 S 
                 10.94 
               
               
                 7 
                 D 
                 −34.09 
                 D 
                 −14.01 
                 D 
                 −14.01 
                 D 
                 6.07 
               
               
                 8 
                 D 
                 −38.96 
                 S 
                 1.2 
                 S 
                 1.2 
                 D 
                 1.2 
               
               
                 9 
                 D 
                 −43.83 
                 D 
                 −3.67 
                 D 
                 −3.67 
                 D 
                 −3.67 
               
               
                 10 
                 D 
                 −48.7 
                 D 
                 −8.54 
                 D 
                 −8.54 
                 S 
                 11.54 
               
               
                 11 
                 D 
                 −53.57 
                 D 
                 −13.41 
                 D 
                 −13.41 
                 D 
                 6.67 
               
               
                 12 
                 D 
                 −58.44 
                 S 
                 1.8 
                 S 
                 1.8 
                 D 
                 1.8 
               
               
                 13 
                 D 
                 −63.31 
                 D 
                 −3.07 
                 D 
                 −3.07 
                 D 
                 −3.07 
               
               
                 14 
                 D 
                 −68.18 
                 D 
                 −7.94 
                 D 
                 −7.94 
                 S 
                 12.14 
               
               
                 15 
                 D 
                 −73.05 
                 D 
                 −12.81 
                 D 
                 −12.81 
                 D 
                 7.27 
               
               
                 16 
                 D 
                 −77.92 
                 S 
                 2.4 
                 S 
                 2.4 
                 D 
                 2.4 
               
               
                 17 
                 D 
                 −82.79 
                 D 
                 −2.47 
                 D 
                 −2.47 
                 D 
                 −2.47 
               
               
                 18 
                 D 
                 −87.66 
                 D 
                 −7.34 
                 D 
                 −7.34 
                 S 
                 12.74 
               
               
                 19 
                 D 
                 −92.53 
                 D 
                 −12.21 
                 D 
                 −12.21 
                 D 
                 7.87 
               
               
                 20 
                 D 
                 −97.4 
                 S 
                 3 
                 S 
                 3 
                 D 
                 3 
               
               
                 21 
                 D 
                 −102.27 
                 D 
                 −1.87 
                 D 
                 −1.87 
                 D 
                 −1.87 
               
               
                 22 
                 D 
                 −107.14 
                 D 
                 −6.74 
                 D 
                 −6.74 
                 S 
                 13.34 
               
               
                 23 
                 D 
                 −112.01 
                 D 
                 −11.61 
                 D 
                 −11.61 
                 D 
                 8.47 
               
               
                 24 
                 D 
                 −116.88 
                 S 
                 3.6 
                 S 
                 3.6 
                 D 
                 3.6 
               
               
                 25 
                 S 
                 −101.67 
                 D 
                 −1.27 
                 D 
                 −1.27 
                 D 
                 −1.27 
               
               
                 26 
                 S 
                 −86.46 
                 D 
                 −6.14 
                 D 
                 −6.14 
                 S 
                 13.94 
               
               
                 27 
                 S 
                 −71.25 
                 D 
                 −11.01 
                 D 
                 −11.01 
                 D 
                 9.07 
               
               
                 28 
                 S 
                 −56.04 
                 S 
                 4.2 
                 S 
                 4.2 
                 D 
                 4.2 
               
               
                 29 
                 S 
                 −40.83 
                 D 
                 −0.67 
                 D 
                 −0.67 
                 D 
                 −0.67 
               
               
                 30 
                 S 
                 −25.62 
                 D 
                 −5.54 
                 D 
                 −5.54 
                 D 
                 −5.54 
               
               
                 31 
                 S 
                 −10.41 
                 D 
                 −10.41 
                 D 
                 −10.41 
                 S 
                 9.67 
               
               
                 32 
                 S 
                 4.8 
                 S 
                 4.8 
                 D 
                 −15.28 
                 D 
                 4.8 
               
               
                 33 
                 D 
                 −0.07 
                 D 
                 −0.07 
                 S 
                 −0.07 
                 D 
                 −0.07 
               
               
                 34 
                 D 
                 −4.94 
                 D 
                 −4.94 
                 D 
                 −4.94 
                 D 
                 −4.94 
               
               
                 35 
                 D 
                 −9.81 
                 D 
                 −9.81 
                 D 
                 −9.81 
                 S 
                 10.27 
               
               
                 36 
                 D 
                 −14.68 
                 S 
                 5.4 
                 D 
                 −14.68 
                 D 
                 5.4 
               
               
                 37 
                 D 
                 −19.55 
                 D 
                 0.53 
                 S 
                 0.53 
                 D 
                 0.53 
               
               
                 38 
                 D 
                 −24.42 
                 D 
                 −4.34 
                 D 
                 −4.34 
                 D 
                 −4.34 
               
               
                 39 
                 D 
                 −29.29 
                 D 
                 −9.21 
                 D 
                 −9.21 
                 S 
                 10.87 
               
               
                 40 
                 D 
                 −34.16 
                 S 
                 6 
                 D 
                 −14.08 
                 D 
                 6 
               
               
                 41 
                 D 
                 −39.03 
                 D 
                 1.13 
                 S 
                 1.13 
                 D 
                 1.13 
               
               
                 42 
                 D 
                 −43.9 
                 D 
                 −3.74 
                 D 
                 −3.74 
                 D 
                 −3.74 
               
               
                 43 
                 D 
                 −48.77 
                 D 
                 −8.61 
                 D 
                 −8.61 
                 S 
                 11.47 
               
               
                 44 
                 D 
                 −53.64 
                 S 
                 6.6 
                 D 
                 −13.48 
                 D 
                 6.6 
               
               
                 45 
                 D 
                 −58.51 
                 D 
                 1.73 
                 S 
                 1.73 
                 D 
                 1.73 
               
               
                 46 
                 D 
                 −63.38 
                 D 
                 −3.14 
                 D 
                 −3.14 
                 D 
                 −3.14 
               
               
                 47 
                 D 
                 −68.25 
                 D 
                 −8.01 
                 D 
                 −8.01 
                 S 
                 12.07 
               
               
                 48 
                 D 
                 −73.12 
                 S 
                 7.2 
                 D 
                 −12.88 
                 D 
                 7.2 
               
               
                 49 
                 D 
                 −77.99 
                 D 
                 2.33 
                 S 
                 2.33 
                 D 
                 2.33 
               
               
                 50 
                 D 
                 −82.86 
                 D 
                 −2.54 
                 D 
                 −2.54 
                 D 
                 −2.54 
               
               
                 51 
                 D 
                 −87.73 
                 D 
                 −7.41 
                 D 
                 −7.41 
                 S 
                 12.67 
               
               
                 52 
                 D 
                 −92.6 
                 S 
                 7.8 
                 D 
                 −12.28 
                 D 
                 7.8 
               
               
                 53 
                 D 
                 −97.47 
                 D 
                 2.93 
                 S 
                 2.93 
                 D 
                 2.93 
               
               
                 54 
                 D 
                 −102.34 
                 D 
                 −1.94 
                 D 
                 −1.94 
                 D 
                 −1.94 
               
               
                 55 
                 D 
                 −107.21 
                 D 
                 −6.81 
                 D 
                 −6.81 
                 S 
                 13.27 
               
               
                 56 
                 D 
                 −112.08 
                 S 
                 8.4 
                 D 
                 −11.68 
                 D 
                 8.4 
               
               
                 57 
                 S 
                 −96.87 
                 D 
                 3.53 
                 S 
                 3.53 
                 D 
                 3.53 
               
               
                 58 
                 S 
                 −81.66 
                 D 
                 −1.34 
                 D 
                 −1.34 
                 D 
                 −1.34 
               
               
                 59 
                 S 
                 −66.45 
                 D 
                 −6.21 
                 D 
                 −6.21 
                 D 
                 −6.21 
               
               
                 60 
                 S 
                 −51.24 
                 S 
                 9 
                 D 
                 −11.08 
                 S 
                 9 
               
               
                 61 
                 S 
                 −36.03 
                 D 
                 4.13 
                 D 
                 −15.95 
                 D 
                 4.13 
               
               
                 62 
                 S 
                 −20.82 
                 D 
                 −0.74 
                 S 
                 −0.74 
                 D 
                 −0.74 
               
               
                 63 
                 S 
                 −5.61 
                 D 
                 −5.61 
                 D 
                 −5.61 
                 D 
                 −5.61 
               
               
                 64 
                 S 
                 9.6 
                 S 
                 9.6 
                 D 
                 −10.48 
                 S 
                 9.6 
               
               
                 65 
                 D 
                 4.73 
                 D 
                 4.73 
                 D 
                 −15.35 
                 D 
                 4.73 
               
               
                 66 
                 D 
                 −0.14 
                 D 
                 −0.14 
                 S 
                 −0.14 
                 D 
                 −0.14 
               
               
                 67 
                 D 
                 −5.01 
                 D 
                 −5.01 
                 D 
                 −5.01 
                 D 
                 −5.01 
               
               
                 68 
                 D 
                 −9.88 
                 S 
                 10.2 
                 D 
                 −9.88 
                 S 
                 10.2 
               
               
                 69 
                 D 
                 −14.75 
                 D 
                 5.33 
                 D 
                 −14.75 
                 D 
                 5.33 
               
               
                 70 
                 D 
                 −19.62 
                 D 
                 0.46 
                 S 
                 0.46 
                 D 
                 0.46 
               
               
                 71 
                 D 
                 −24.49 
                 D 
                 −4.41 
                 D 
                 −4.41 
                 D 
                 −4.41 
               
               
                 72 
                 D 
                 −29.36 
                 S 
                 10.8 
                 D 
                 −9.28 
                 S 
                 10.8 
               
               
                 73 
                 D 
                 −34.23 
                 D 
                 5.93 
                 D 
                 −14.15 
                 D 
                 5.93 
               
               
                 74 
                 D 
                 −39.1 
                 D 
                 1.06 
                 S 
                 1.06 
                 D 
                 1.06 
               
               
                 75 
                 D 
                 −43.97 
                 D 
                 −3.81 
                 D 
                 −3.81 
                 D 
                 −3.81 
               
               
                 76 
                 D 
                 −48.84 
                 S 
                 11.4 
                 D 
                 −8.68 
                 S 
                 11.4 
               
               
                 77 
                 D 
                 −53.71 
                 D 
                 6.53 
                 D 
                 −13.55 
                 D 
                 6.53 
               
               
                 78 
                 D 
                 −58.58 
                 D 
                 1.66 
                 S 
                 1.66 
                 D 
                 1.66 
               
               
                 79 
                 D 
                 −63.45 
                 D 
                 −3.21 
                 D 
                 −3.21 
                 D 
                 −3.21 
               
               
                 80 
                 D 
                 −68.32 
                 S 
                 12 
                 D 
                 −8.08 
                 S 
                 12 
               
               
                 81 
                 D 
                 −73.19 
                 D 
                 7.13 
                 D 
                 −12.95 
                 D 
                 7.13 
               
               
                 82 
                 D 
                 −78.06 
                 D 
                 2.26 
                 S 
                 2.26 
                 D 
                 2.26 
               
               
                 83 
                 D 
                 −82.93 
                 D 
                 −2.61 
                 D 
                 −2.61 
                 D 
                 −2.61 
               
               
                 84 
                 D 
                 −87.8 
                 S 
                 12.6 
                 D 
                 −7.48 
                 S 
                 12.6 
               
               
                 85 
                 D 
                 −92.67 
                 D 
                 7.73 
                 D 
                 −12.35 
                 D 
                 7.73 
               
               
                 86 
                 D 
                 −97.54 
                 D 
                 2.86 
                 S 
                 2.86 
                 D 
                 2.86 
               
               
                 87 
                 D 
                 −102.41 
                 D 
                 −2.01 
                 D 
                 −2.01 
                 D 
                 −2.01 
               
               
                 88 
                 D 
                 −107.28 
                 S 
                 13.2 
                 D 
                 −6.88 
                 S 
                 13.2 
               
               
                 89 
                 S 
                 −92.07 
                 D 
                 8.33 
                 D 
                 −11.75 
                 D 
                 8.33 
               
               
                 90 
                 S 
                 −76.86 
                 D 
                 3.46 
                 S 
                 3.46 
                 D 
                 3.46 
               
               
                 91 
                 S 
                 −61.65 
                 D 
                 −1.41 
                 D 
                 −1.41 
                 D 
                 −1.41 
               
               
                 92 
                 S 
                 −46.44 
                 S 
                 13.8 
                 D 
                 −6.28 
                 D 
                 −6.28 
               
               
                 93 
                 S 
                 −31.23 
                 D 
                 8.93 
                 D 
                 −11.15 
                 S 
                 8.93 
               
               
                 94 
                 S 
                 −16.02 
                 D 
                 4.06 
                 D 
                 −16.02 
                 D 
                 4.06 
               
               
                 95 
                 S 
                 −0.81 
                 D 
                 −0.81 
                 S 
                 −0.81 
                 D 
                 −0.81 
               
               
                 96 
                 S 
                 14.4 
                 S 
                 14.4 
                 D 
                 −5.68 
                 D 
                 −5.68 
               
               
                 97 
                 D 
                 9.53 
                 D 
                 9.53 
                 D 
                 −10.55 
                 S 
                 9.53 
               
               
                 98 
                 D 
                 4.66 
                 D 
                 4.66 
                 D 
                 −15.42 
                 D 
                 4.66 
               
               
                 99 
                 D 
                 −0.21 
                 D 
                 −0.21 
                 S 
                 −0.21 
                 D 
                 −0.21 
               
               
                 100 
                 D 
                 −5.08 
                 S 
                 15 
                 D 
                 −5.08 
                 D 
                 −5.08 
               
               
                 101 
                 D 
                 −9.95 
                 D 
                 10.13 
                 D 
                 −9.95 
                 S 
                 10.13 
               
               
                 102 
                 D 
                 −14.82 
                 D 
                 5.26 
                 D 
                 −14.82 
                 D 
                 5.26 
               
               
                 103 
                 D 
                 −19.69 
                 D 
                 0.39 
                 S 
                 0.39 
                 D 
                 0.39 
               
               
                 104 
                 D 
                 −24.56 
                 S 
                 15.6 
                 D 
                 −4.48 
                 D 
                 −4.48 
               
               
                 105 
                 D 
                 −29.43 
                 D 
                 10.73 
                 D 
                 −9.35 
                 S 
                 10.73 
               
               
                 106 
                 D 
                 −34.3 
                 D 
                 5.86 
                 D 
                 −14.22 
                 D 
                 5.86 
               
               
                 107 
                 D 
                 −39.17 
                 D 
                 0.99 
                 S 
                 0.99 
                 D 
                 0.99 
               
               
                 108 
                 D 
                 −44.04 
                 S 
                 16.2 
                 D 
                 −3.88 
                 D 
                 −3.88 
               
               
                 109 
                 D 
                 −48.91 
                 D 
                 11.33 
                 D 
                 −8.75 
                 S 
                 11.33 
               
               
                 110 
                 D 
                 −53.78 
                 D 
                 6.46 
                 D 
                 −13.62 
                 D 
                 6.46 
               
               
                 111 
                 D 
                 −58.65 
                 D 
                 1.59 
                 S 
                 1.59 
                 D 
                 1.59 
               
               
                 112 
                 D 
                 −63.52 
                 S 
                 16.8 
                 D 
                 −3.28 
                 D 
                 −3.28 
               
               
                 113 
                 D 
                 −68.39 
                 D 
                 11.93 
                 D 
                 −8.15 
                 S 
                 11.93 
               
               
                 114 
                 D 
                 −73.26 
                 D 
                 7.06 
                 D 
                 −13.02 
                 D 
                 7.06 
               
               
                 115 
                 D 
                 −78.13 
                 D 
                 2.19 
                 S 
                 2.19 
                 D 
                 2.19 
               
               
                 116 
                 D 
                 −83 
                 S 
                 17.4 
                 D 
                 −2.68 
                 D 
                 −2.68 
               
               
                 117 
                 D 
                 −87.87 
                 D 
                 12.53 
                 D 
                 −7.55 
                 S 
                 12.53 
               
               
                 118 
                 D 
                 −92.74 
                 D 
                 7.66 
                 D 
                 −12.42 
                 D 
                 7.66 
               
               
                 119 
                 D 
                 −97.61 
                 D 
                 2.79 
                 S 
                 2.79 
                 D 
                 2.79 
               
               
                 120 
                 D 
                 −102.48 
                 S 
                 18 
                 D 
                 −2.08 
                 D 
                 −2.08 
               
               
                 121 
                 S 
                 −87.27 
                 D 
                 13.13 
                 D 
                 −6.95 
                 D 
                 −6.95 
               
               
                 122 
                 S 
                 −72.06 
                 D 
                 8.26 
                 D 
                 −11.82 
                 S 
                 8.26 
               
               
                 123 
                 S 
                 −56.85 
                 D 
                 3.39 
                 D 
                 −16.69 
                 D 
                 3.39 
               
               
                 124 
                 S 
                 −41.64 
                 S 
                 18.6 
                 S 
                 −1.48 
                 D 
                 −1.48 
               
               
                 125 
                 S 
                 −26.43 
                 D 
                 13.73 
                 D 
                 −6.35 
                 D 
                 −6.35 
               
               
                 126 
                 S 
                 −11.22 
                 D 
                 8.86 
                 D 
                 −11.22 
                 S 
                 8.86 
               
               
                 127 
                 S 
                 3.99 
                 D 
                 3.99 
                 D 
                 −16.09 
                 D 
                 3.99 
               
               
                 128 
                 S 
                 19.2 
                 S 
                 19.2 
                 S 
                 −0.88 
                 D 
                 −0.88 
               
               
                 129 
                 D 
                 14.33 
                 D 
                 14.33 
                 D 
                 −5.75 
                 D 
                 −5.75 
               
               
                 130 
                 D 
                 9.46 
                 D 
                 9.46 
                 D 
                 −10.62 
                 S 
                 9.46 
               
               
                 131 
                 D 
                 4.59 
                 D 
                 4.59 
                 D 
                 −15.49 
                 D 
                 4.59 
               
               
                 132 
                 D 
                 −0.28 
                 S 
                 19.8 
                 S 
                 −0.28 
                 D 
                 −0.28 
               
               
                 133 
                 D 
                 −5.15 
                 D 
                 14.93 
                 D 
                 −5.15 
                 D 
                 −5.15 
               
               
                 134 
                 D 
                 −10.02 
                 D 
                 10.06 
                 D 
                 −10.02 
                 S 
                 10.06 
               
               
                 135 
                 D 
                 −14.89 
                 D 
                 5.19 
                 D 
                 −14.89 
                 D 
                 5.19 
               
               
                 136 
                 D 
                 −19.76 
                 S 
                 20.4 
                 S 
                 0.32 
                 D 
                 0.32 
               
               
                 137 
                 D 
                 −24.63 
                 D 
                 15.53 
                 D 
                 −4.55 
                 D 
                 −4.55 
               
               
                 138 
                 D 
                 −29.5 
                 D 
                 10.66 
                 D 
                 −9.42 
                 S 
                 10.66 
               
               
                 139 
                 D 
                 −34.37 
                 D 
                 5.79 
                 D 
                 −14.29 
                 D 
                 5.79 
               
               
                 140 
                 D 
                 −39.24 
                 S 
                 21 
                 S 
                 0.92 
                 D 
                 0.92 
               
               
                 141 
                 D 
                 −44.11 
                 D 
                 16.13 
                 D 
                 −3.95 
                 D 
                 −3.95 
               
               
                 142 
                 D 
                 −48.98 
                 D 
                 11.26 
                 D 
                 −8.82 
                 S 
                 11.26 
               
               
                 143 
                 D 
                 −53.85 
                 D 
                 6.39 
                 D 
                 −13.69 
                 D 
                 6.39 
               
               
                 144 
                 D 
                 −58.72 
                 S 
                 21.6 
                 S 
                 1.52 
                 D 
                 1.52 
               
               
                 145 
                 D 
                 −63.59 
                 D 
                 16.73 
                 D 
                 −3.35 
                 D 
                 −3.35 
               
               
                 146 
                 D 
                 −68.46 
                 D 
                 11.86 
                 D 
                 −8.22 
                 S 
                 11.86 
               
               
                 147 
                 D 
                 −73.33 
                 D 
                 6.99 
                 D 
                 −13.09 
                 D 
                 6.99 
               
               
                 148 
                 D 
                 −78.2 
                 S 
                 22.2 
                 S 
                 2.12 
                 D 
                 2.12 
               
               
                 149 
                 D 
                 −83.07 
                 D 
                 17.33 
                 D 
                 −2.75 
                 D 
                 −2.75 
               
               
                 150 
                 D 
                 −87.94 
                 D 
                 12.46 
                 D 
                 −7.62 
                 S 
                 12.46 
               
               
                 151 
                 D 
                 −92.81 
                 D 
                 7.59 
                 D 
                 −12.49 
                 D 
                 7.59 
               
               
                 152 
                 D 
                 −97.68 
                 S 
                 22.8 
                 S 
                 2.72 
                 D 
                 2.72 
               
               
                 153 
                 S 
                 −82.47 
                 D 
                 17.93 
                 D 
                 −2.15 
                 D 
                 −2.15 
               
               
                 154 
                 S 
                 −67.26 
                 D 
                 13.06 
                 D 
                 −7.02 
                 D 
                 −7.02 
               
               
                 155 
                 S 
                 −52.05 
                 D 
                 8.19 
                 D 
                 −11.89 
                 S 
                 8.19 
               
               
                 156 
                 S 
                 −36.84 
                 S 
                 23.4 
                 D 
                 −16.76 
                 D 
                 3.32 
               
               
                 157 
                 S 
                 −21.63 
                 D 
                 18.53 
                 S 
                 −1.55 
                 D 
                 −1.55 
               
               
                 158 
                 S 
                 −6.42 
                 D 
                 13.66 
                 D 
                 −6.42 
                 D 
                 −6.42 
               
               
                 159 
                 S 
                 8.79 
                 D 
                 8.79 
                 D 
                 −11.29 
                 S 
                 8.79 
               
               
                 160 
                 S 
                 24 
                 S 
                 24 
                 D 
                 −16.16 
                 D 
                 3.92 
               
               
                 161 
                 D 
                 19.13 
                 D 
                 19.13 
                 S 
                 −0.95 
                 D 
                 −0.95 
               
               
                 162 
                 D 
                 14.26 
                 D 
                 14.26 
                 D 
                 −5.82 
                 D 
                 −5.82 
               
               
                 163 
                 D 
                 9.39 
                 D 
                 9.39 
                 D 
                 −10.69 
                 S 
                 9.39 
               
               
                 164 
                 D 
                 4.52 
                 S 
                 24.6 
                 D 
                 −15.56 
                 D 
                 4.52 
               
               
                 165 
                 D 
                 −0.35 
                 D 
                 19.73 
                 S 
                 −0.35 
                 D 
                 −0.35 
               
               
                 166 
                 D 
                 −5.22 
                 D 
                 14.86 
                 D 
                 −5.22 
                 D 
                 −5.22 
               
               
                 167 
                 D 
                 −10.09 
                 D 
                 9.99 
                 D 
                 −10.09 
                 S 
                 9.99 
               
               
                 168 
                 D 
                 −14.96 
                 S 
                 25.2 
                 D 
                 −14.96 
                 D 
                 5.12 
               
               
                 169 
                 D 
                 −19.83 
                 D 
                 20.33 
                 S 
                 0.25 
                 D 
                 0.25 
               
               
                 170 
                 D 
                 −24.7 
                 D 
                 15.46 
                 D 
                 −4.62 
                 D 
                 −4.62 
               
               
                 171 
                 D 
                 −29.57 
                 D 
                 10.59 
                 D 
                 −9.49 
                 S 
                 10.59 
               
               
                 172 
                 D 
                 −34.44 
                 S 
                 25.8 
                 D 
                 −14.36 
                 D 
                 5.72 
               
               
                 173 
                 D 
                 −39.31 
                 D 
                 20.93 
                 S 
                 0.85 
                 D 
                 0.85 
               
               
                 174 
                 D 
                 −44.18 
                 D 
                 16.06 
                 D 
                 −4.02 
                 D 
                 −4.02 
               
               
                 175 
                 D 
                 −49.05 
                 D 
                 11.19 
                 D 
                 −8.89 
                 S 
                 11.19 
               
               
                 176 
                 D 
                 −53.92 
                 S 
                 26.4 
                 D 
                 −13.76 
                 D 
                 6.32 
               
               
                 177 
                 D 
                 −58.79 
                 D 
                 21.53 
                 S 
                 1.45 
                 D 
                 1.45 
               
               
                 178 
                 D 
                 −63.66 
                 D 
                 16.66 
                 D 
                 −3.42 
                 D 
                 −3.42 
               
               
                 179 
                 D 
                 −68.53 
                 D 
                 11.79 
                 D 
                 −8.29 
                 S 
                 11.79 
               
               
                 180 
                 D 
                 −73.4 
                 S 
                 27 
                 D 
                 −13.16 
                 D 
                 6.92 
               
               
                 181 
                 D 
                 −78.27 
                 D 
                 22.13 
                 S 
                 2.05 
                 D 
                 2.05 
               
               
                 182 
                 D 
                 −83.14 
                 D 
                 17.26 
                 D 
                 −2.82 
                 D 
                 −2.82 
               
               
                 183 
                 D 
                 −88.01 
                 D 
                 12.39 
                 D 
                 −7.69 
                 D 
                 −7.69 
               
               
                 184 
                 D 
                 −92.88 
                 S 
                 27.6 
                 D 
                 −12.56 
                 S 
                 7.52 
               
               
                 185 
                 S 
                 −77.67 
                 D 
                 22.73 
                 D 
                 −17.43 
                 D 
                 2.65 
               
               
                 186 
                 S 
                 −62.46 
                 D 
                 17.86 
                 S 
                 −2.22 
                 D 
                 −2.22 
               
               
                 187 
                 S 
                 −47.25 
                 D 
                 12.99 
                 D 
                 −7.09 
                 D 
                 −7.09 
               
               
                 188 
                 S 
                 −32.04 
                 S 
                 28.2 
                 D 
                 −11.96 
                 S 
                 8.12 
               
               
                 189 
                 S 
                 −16.83 
                 D 
                 23.33 
                 D 
                 −16.83 
                 D 
                 3.25 
               
               
                 190 
                 S 
                 −1.62 
                 D 
                 18.46 
                 S 
                 −1.62 
                 D 
                 −1.62 
               
               
                 191 
                 S 
                 13.59 
                 D 
                 13.59 
                 D 
                 −6.49 
                 D 
                 −6.49 
               
               
                 192 
                 S 
                 28.8 
                 S 
                 28.8 
                 D 
                 −11.36 
                 S 
                 8.72 
               
               
                 193 
                 D 
                 23.93 
                 D 
                 23.93 
                 D 
                 −16.23 
                 D 
                 3.85 
               
               
                 194 
                 D 
                 19.06 
                 D 
                 19.06 
                 S 
                 −1.02 
                 D 
                 −1.02 
               
               
                 195 
                 D 
                 14.19 
                 D 
                 14.19 
                 D 
                 −5.89 
                 D 
                 −5.89 
               
               
                 196 
                 D 
                 9.32 
                 S 
                 29.4 
                 D 
                 −10.76 
                 S 
                 9.32 
               
               
                 197 
                 D 
                 4.45 
                 D 
                 24.53 
                 D 
                 −15.63 
                 D 
                 4.45 
               
               
                 198 
                 D 
                 −0.42 
                 D 
                 19.66 
                 S 
                 −0.42 
                 D 
                 −0.42 
               
               
                 199 
                 D 
                 −5.29 
                 D 
                 14.79 
                 D 
                 −5.29 
                 D 
                 −5.29 
               
               
                 200 
                 D 
                 −10.16 
                 S 
                 30 
                 D 
                 −10.16 
                 S 
                 9.92 
               
               
                 201 
                 D 
                 −15.03 
                 D 
                 25.13 
                 D 
                 −15.03 
                 D 
                 5.05 
               
               
                 202 
                 D 
                 −19.9 
                 D 
                 20.26 
                 S 
                 0.18 
                 D 
                 0.18 
               
               
                 203 
                 D 
                 −24.77 
                 D 
                 15.39 
                 D 
                 −4.69 
                 D 
                 −4.69 
               
               
                 204 
                 D 
                 −29.64 
                 S 
                 30.6 
                 D 
                 −9.56 
                 S 
                 10.52 
               
               
                 205 
                 D 
                 −34.51 
                 D 
                 25.73 
                 D 
                 −14.43 
                 D 
                 5.65 
               
               
                 206 
                 D 
                 −39.38 
                 D 
                 20.86 
                 S 
                 0.78 
                 D 
                 0.78 
               
               
                 207 
                 D 
                 −44.25 
                 D 
                 15.99 
                 D 
                 −4.09 
                 D 
                 −4.09 
               
               
                 208 
                 D 
                 −49.12 
                 S 
                 31.2 
                 D 
                 −8.96 
                 S 
                 11.12 
               
               
                 209 
                 D 
                 −53.99 
                 D 
                 26.33 
                 D 
                 −13.83 
                 D 
                 6.25 
               
               
                 210 
                 D 
                 −58.86 
                 D 
                 21.46 
                 S 
                 1.38 
                 D 
                 1.38 
               
               
                 211 
                 D 
                 −63.73 
                 D 
                 16.59 
                 D 
                 −3.49 
                 D 
                 −3.49 
               
               
                 212 
                 D 
                 −68.6 
                 S 
                 31.8 
                 D 
                 −8.36 
                 D 
                 −8.36 
               
               
                 213 
                 D 
                 −73.47 
                 D 
                 26.93 
                 D 
                 −13.23 
                 S 
                 6.85 
               
               
                 214 
                 D 
                 −78.34 
                 D 
                 22.06 
                 D 
                 −18.1 
                 D 
                 1.98 
               
               
                 215 
                 D 
                 −83.21 
                 D 
                 17.19 
                 S 
                 −2.89 
                 D 
                 −2.89 
               
               
                 216 
                 D 
                 −88.08 
                 S 
                 32.4 
                 D 
                 −7.76 
                 D 
                 −7.76 
               
               
                 217 
                 S 
                 −72.87 
                 D 
                 27.53 
                 D 
                 −12.63 
                 S 
                 7.45 
               
               
                 218 
                 S 
                 −57.66 
                 D 
                 22.66 
                 D 
                 −17.5 
                 D 
                 2.58 
               
               
                 219 
                 S 
                 −42.45 
                 D 
                 17.79 
                 S 
                 −2.29 
                 D 
                 −2.29 
               
               
                 220 
                 S 
                 −27.24 
                 S 
                 33 
                 D 
                 −7.16 
                 D 
                 −7.16 
               
               
                 221 
                 S 
                 −12.03 
                 D 
                 28.13 
                 D 
                 −12.03 
                 S 
                 8.05 
               
               
                 222 
                 S 
                 3.18 
                 D 
                 23.26 
                 D 
                 −16.9 
                 D 
                 3.18 
               
               
                 223 
                 S 
                 18.39 
                 D 
                 18.39 
                 S 
                 −1.69 
                 D 
                 −1.69 
               
               
                 224 
                 S 
                 33.6 
                 S 
                 33.6 
                 D 
                 −6.56 
                 D 
                 −6.56 
               
               
                 225 
                 D 
                 28.73 
                 D 
                 28.73 
                 D 
                 −11.43 
                 S 
                 8.65 
               
               
                 226 
                 D 
                 23.86 
                 D 
                 23.86 
                 D 
                 −16.3 
                 D 
                 3.78 
               
               
                 227 
                 D 
                 18.99 
                 D 
                 18.99 
                 S 
                 −1.09 
                 D 
                 −1.09 
               
               
                 228 
                 D 
                 14.12 
                 S 
                 34.2 
                 D 
                 −5.96 
                 D 
                 −5.96 
               
               
                 229 
                 D 
                 9.25 
                 D 
                 29.33 
                 D 
                 −10.83 
                 S 
                 9.25 
               
               
                 230 
                 D 
                 4.38 
                 D 
                 24.46 
                 D 
                 −15.7 
                 D 
                 4.38 
               
               
                 231 
                 D 
                 −0.49 
                 D 
                 19.59 
                 S 
                 −0.49 
                 D 
                 −0.49 
               
               
                 232 
                 D 
                 −5.36 
                 S 
                 34.8 
                 D 
                 −5.36 
                 D 
                 −5.36 
               
               
                 233 
                 D 
                 −10.23 
                 D 
                 29.93 
                 D 
                 −10.23 
                 S 
                 9.85 
               
               
                 234 
                 D 
                 −15.1 
                 D 
                 25.06 
                 D 
                 −15.1 
                 D 
                 4.98 
               
               
                 235 
                 D 
                 −19.97 
                 D 
                 20.19 
                 S 
                 0.11 
                 D 
                 0.11 
               
               
                 236 
                 D 
                 −24.84 
                 S 
                 35.4 
                 D 
                 −4.76 
                 D 
                 −4.76 
               
               
                 237 
                 D 
                 −29.71 
                 D 
                 30.53 
                 D 
                 −9.63 
                 S 
                 10.45 
               
               
                 238 
                 D 
                 −34.58 
                 D 
                 25.66 
                 D 
                 −14.5 
                 D 
                 5.58 
               
               
                 239 
                 D 
                 −39.45 
                 D 
                 20.79 
                 S 
                 0.71 
                 D 
                 0.71 
               
               
                 240 
                 D 
                 −44.32 
                 S 
                 36 
                 D 
                 −4.16 
                 D 
                 −4.16 
               
               
                 241 
                 D 
                 −49.19 
                 D 
                 31.13 
                 D 
                 −9.03 
                 S 
                 11.05 
               
               
                 242 
                 D 
                 −54.06 
                 D 
                 26.26 
                 D 
                 −13.9 
                 D 
                 6.18 
               
               
                 243 
                 D 
                 −58.93 
                 D 
                 21.39 
                 S 
                 1.31 
                 D 
                 1.31 
               
               
                 244 
                 D 
                 −63.8 
                 S 
                 36.6 
                 D 
                 −3.56 
                 D 
                 −3.56 
               
               
                 245 
                 D 
                 −68.67 
                 D 
                 31.73 
                 D 
                 −8.43 
                 D 
                 −8.43 
               
               
                 246 
                 D 
                 −73.54 
                 D 
                 26.86 
                 D 
                 −13.3 
                 S 
                 6.78 
               
               
                 247 
                 D 
                 −78.41 
                 D 
                 21.99 
                 D 
                 −18.17 
                 D 
                 1.91 
               
               
                 248 
                 D 
                 −83.28 
                 S 
                 37.2 
                 S 
                 −2.96 
                 D 
                 −2.96 
               
               
                 249 
                 S 
                 −68.07 
                 D 
                 32.33 
                 D 
                 −7.83 
                 D 
                 −7.83 
               
               
                 250 
                 S 
                 −52.86 
                 D 
                 27.46 
                 D 
                 −12.7 
                 S 
                 7.38 
               
               
                 251 
                 S 
                 −37.65 
                 D 
                 22.59 
                 D 
                 −17.57 
                 D 
                 2.51 
               
               
                 252 
                 S 
                 −22.44 
                 S 
                 37.8 
                 S 
                 −2.36 
                 D 
                 −2.36 
               
               
                 253 
                 S 
                 −7.23 
                 D 
                 32.93 
                 D 
                 −7.23 
                 D 
                 −7.23 
               
               
                 254 
                 S 
                 7.98 
                 D 
                 28.06 
                 D 
                 −12.1 
                 S 
                 7.98 
               
               
                 255 
                 S 
                 23.19 
                 D 
                 23.19 
                 D 
                 −16.97 
                 D 
                 3.11 
               
               
                 256 
                 S 
                 38.4 
                 S 
                 38.4 
                 S 
                 −1.76 
                 D 
                 −1.76 
               
               
                 257 
                 D 
                 33.53 
                 D 
                 33.53 
                 D 
                 −6.63 
                 D 
                 −6.63 
               
               
                 258 
                 D 
                 28.66 
                 D 
                 28.66 
                 D 
                 −11.5 
                 S 
                 8.58 
               
               
                 259 
                 D 
                 23.79 
                 D 
                 23.79 
                 D 
                 −16.37 
                 D 
                 3.71 
               
               
                 260 
                 D 
                 18.92 
                 S 
                 39 
                 S 
                 −1.16 
                 D 
                 −1.16 
               
               
                 261 
                 D 
                 14.05 
                 D 
                 34.13 
                 D 
                 −6.03 
                 D 
                 −6.03 
               
               
                 262 
                 D 
                 9.18 
                 D 
                 29.26 
                 D 
                 −10.9 
                 S 
                 9.18 
               
               
                 263 
                 D 
                 4.31 
                 D 
                 24.39 
                 D 
                 −15.77 
                 D 
                 4.31 
               
               
                 264 
                 D 
                 −0.56 
                 S 
                 39.6 
                 S 
                 −0.56 
                 D 
                 −0.56 
               
               
                 265 
                 D 
                 −5.43 
                 D 
                 34.73 
                 D 
                 −5.43 
                 D 
                 −5.43 
               
               
                 266 
                 D 
                 −10.3 
                 D 
                 29.86 
                 D 
                 −10.3 
                 S 
                 9.78 
               
               
                 267 
                 D 
                 −15.17 
                 D 
                 24.99 
                 D 
                 −15.17 
                 D 
                 4.91 
               
               
                 268 
                 D 
                 −20.04 
                 S 
                 40.2 
                 S 
                 0.04 
                 D 
                 0.04 
               
               
                 269 
                 D 
                 −24.91 
                 D 
                 35.33 
                 D 
                 −4.83 
                 D 
                 −4.83 
               
               
                 270 
                 D 
                 −29.78 
                 D 
                 30.46 
                 D 
                 −9.7 
                 S 
                 10.38 
               
               
                 271 
                 D 
                 −34.65 
                 D 
                 25.59 
                 D 
                 −14.57 
                 D 
                 5.51 
               
               
                 272 
                 D 
                 −39.52 
                 S 
                 40.8 
                 S 
                 0.64 
                 D 
                 0.64 
               
               
                 273 
                 D 
                 −44.39 
                 D 
                 35.93 
                 D 
                 −4.23 
                 D 
                 −4.23 
               
               
                 274 
                 D 
                 −49.26 
                 D 
                 31.06 
                 D 
                 −9.1 
                 D 
                 −9.1 
               
               
                 275 
                 D 
                 −54.13 
                 D 
                 26.19 
                 D 
                 −13.97 
                 S 
                 6.11 
               
               
                 276 
                 D 
                 −59 
                 S 
                 41.4 
                 D 
                 −18.84 
                 D 
                 1.24 
               
               
                 277 
                 D 
                 −63.87 
                 D 
                 36.53 
                 S 
                 −3.63 
                 D 
                 −3.63 
               
               
                 278 
                 D 
                 −68.74 
                 D 
                 31.66 
                 D 
                 −8.5 
                 D 
                 −8.5 
               
               
                 279 
                 D 
                 −73.61 
                 D 
                 26.79 
                 D 
                 −13.37 
                 S 
                 6.71 
               
               
                 280 
                 D 
                 −78.48 
                 S 
                 42 
                 D 
                 −18.24 
                 D 
                 1.84 
               
               
                 281 
                 S 
                 −63.27 
                 D 
                 37.13 
                 S 
                 −3.03 
                 D 
                 −3.03 
               
               
                 282 
                 S 
                 −48.06 
                 D 
                 32.26 
                 D 
                 −7.9 
                 D 
                 −7.9 
               
               
                 283 
                 S 
                 −32.85 
                 D 
                 27.39 
                 D 
                 −12.77 
                 S 
                 7.31 
               
               
                 284 
                 S 
                 −17.64 
                 S 
                 42.6 
                 D 
                 −17.64 
                 D 
                 2.44 
               
               
                 285 
                 S 
                 −2.43 
                 D 
                 37.73 
                 S 
                 −2.43 
                 D 
                 −2.43 
               
               
                 286 
                 S 
                 12.78 
                 D 
                 32.86 
                 D 
                 −7.3 
                 D 
                 −7.3 
               
               
                 287 
                 S 
                 27.99 
                 D 
                 27.99 
                 D 
                 −12.17 
                 S 
                 7.91 
               
               
                 288 
                 S 
                 43.2 
                 S 
                 43.2 
                 D 
                 −17.04 
                 D 
                 3.04 
               
               
                 289 
                 D 
                 38.33 
                 D 
                 38.33 
                 S 
                 −1.83 
                 D 
                 −1.83 
               
               
                 290 
                 D 
                 33.46 
                 D 
                 33.46 
                 D 
                 −6.7 
                 D 
                 −6.7 
               
               
                 291 
                 D 
                 28.59 
                 D 
                 28.59 
                 D 
                 −11.57 
                 S 
                 8.51 
               
               
                 292 
                 D 
                 23.72 
                 S 
                 43.8 
                 D 
                 −16.44 
                 D 
                 3.64 
               
               
                 293 
                 D 
                 18.85 
                 D 
                 38.93 
                 S 
                 −1.23 
                 D 
                 −1.23 
               
               
                 294 
                 D 
                 13.98 
                 D 
                 34.06 
                 D 
                 −6.1 
                 D 
                 −6.1 
               
               
                 295 
                 D 
                 9.11 
                 D 
                 29.19 
                 D 
                 −10.97 
                 S 
                 9.11 
               
               
                 296 
                 D 
                 4.24 
                 S 
                 44.4 
                 D 
                 −15.84 
                 D 
                 4.24 
               
               
                 297 
                 D 
                 −0.63 
                 D 
                 39.53 
                 S 
                 −0.63 
                 D 
                 −0.63 
               
               
                 298 
                 D 
                 −5.5 
                 D 
                 34.66 
                 D 
                 −5.5 
                 D 
                 −5.5 
               
               
                 299 
                 D 
                 −10.37 
                 D 
                 29.79 
                 D 
                 −10.37 
                 S 
                 9.71 
               
               
                 300 
                 D 
                 −15.24 
                 S 
                 45 
                 D 
                 −15.24 
                 D 
                 4.84 
               
               
                 301 
                 D 
                 −20.11 
                 D 
                 40.13 
                 S 
                 −0.03 
                 D 
                 −0.03 
               
               
                 302 
                 D 
                 −24.98 
                 D 
                 35.26 
                 D 
                 −4.9 
                 D 
                 −4.9 
               
               
                 303 
                 D 
                 −29.85 
                 D 
                 30.39 
                 D 
                 −9.77 
                 D 
                 −9.77 
               
               
                 304 
                 D 
                 −34.72 
                 S 
                 45.6 
                 D 
                 −14.64 
                 S 
                 5.44 
               
               
                 305 
                 D 
                 −39.59 
                 D 
                 40.73 
                 D 
                 −19.51 
                 D 
                 0.57 
               
               
                 306 
                 D 
                 −44.46 
                 D 
                 35.86 
                 S 
                 −4.3 
                 D 
                 −4.3 
               
               
                 307 
                 D 
                 −49.33 
                 D 
                 30.99 
                 D 
                 −9.17 
                 D 
                 −9.17 
               
               
                 308 
                 D 
                 −54.2 
                 S 
                 46.2 
                 D 
                 −14.04 
                 S 
                 6.04 
               
               
                 309 
                 D 
                 −59.07 
                 D 
                 41.33 
                 D 
                 −18.91 
                 D 
                 1.17 
               
               
                 310 
                 D 
                 −63.94 
                 D 
                 36.46 
                 S 
                 −3.7 
                 D 
                 −3.7 
               
               
                 311 
                 D 
                 −68.81 
                 D 
                 31.59 
                 D 
                 −8.57 
                 D 
                 −8.57 
               
               
                 312 
                 D 
                 −73.68 
                 S 
                 46.8 
                 D 
                 −13.44 
                 S 
                 6.64 
               
               
                 313 
                 S 
                 −58.47 
                 D 
                 41.93 
                 D 
                 −18.31 
                 D 
                 1.77 
               
               
                 314 
                 S 
                 −43.26 
                 D 
                 37.06 
                 S 
                 −3.1 
                 D 
                 −3.1 
               
               
                 315 
                 S 
                 −28.05 
                 D 
                 32.19 
                 D 
                 −7.97 
                 D 
                 −7.97 
               
               
                 316 
                 S 
                 −12.84 
                 S 
                 47.4 
                 D 
                 −12.84 
                 S 
                 7.24 
               
               
                 317 
                 S 
                 2.37 
                 D 
                 42.53 
                 D 
                 −17.71 
                 D 
                 2.37 
               
               
                 318 
                 S 
                 17.58 
                 D 
                 37.66 
                 S 
                 −2.5 
                 D 
                 −2.5 
               
               
                 319 
                 S 
                 32.79 
                 D 
                 32.79 
                 D 
                 −7.37 
                 D 
                 −7.37 
               
               
                 320 
                 S 
                 48 
                 S 
                 48 
                 D 
                 −12.24 
                 S 
                 7.84 
               
               
                 321 
                 D 
                 43.13 
                 D 
                 43.13 
                 D 
                 −17.11 
                 D 
                 2.97 
               
               
                 322 
                 D 
                 38.26 
                 D 
                 38.26 
                 S 
                 −1.9 
                 D 
                 −1.9 
               
               
                 323 
                 D 
                 33.39 
                 D 
                 33.39 
                 D 
                 −6.77 
                 D 
                 −6.77 
               
               
                 324 
                 D 
                 28.52 
                 S 
                 48.6 
                 D 
                 −11.64 
                 S 
                 8.44 
               
               
                 325 
                 D 
                 23.65 
                 D 
                 43.73 
                 D 
                 −16.51 
                 D 
                 3.57 
               
               
                 326 
                 D 
                 18.78 
                 D 
                 38.86 
                 S 
                 −1.3 
                 D 
                 −1.3 
               
               
                 327 
                 D 
                 13.91 
                 D 
                 33.99 
                 D 
                 −6.17 
                 D 
                 −6.17 
               
               
                 328 
                 D 
                 9.04 
                 S 
                 49.2 
                 D 
                 −11.04 
                 S 
                 9.04 
               
               
                 329 
                 D 
                 4.17 
                 D 
                 44.33 
                 D 
                 −15.91 
                 D 
                 4.17 
               
               
                 330 
                 D 
                 −0.7 
                 D 
                 39.46 
                 S 
                 −0.7 
                 D 
                 −0.7 
               
               
                 331 
                 D 
                 −5.57 
                 D 
                 34.59 
                 D 
                 −5.57 
                 D 
                 −5.57 
               
               
                 332 
                 D 
                 −10.44 
                 S 
                 49.8 
                 D 
                 −10.44 
                 S 
                 9.64 
               
               
                 333 
                 D 
                 −15.31 
                 D 
                 44.93 
                 D 
                 −15.31 
                 D 
                 4.77 
               
               
                 334 
                 D 
                 −20.18 
                 D 
                 40.06 
                 S 
                 −0.1 
                 D 
                 −0.1 
               
               
                 335 
                 D 
                 −25.05 
                 D 
                 35.19 
                 D 
                 −4.97 
                 D 
                 −4.97 
               
               
                 336 
                 D 
                 −29.92 
                 S 
                 50.4 
                 D 
                 −9.84 
                 D 
                 −9.84 
               
               
                 337 
                 D 
                 −34.79 
                 D 
                 45.53 
                 D 
                 −14.71 
                 S 
                 5.37 
               
               
                 338 
                 D 
                 −39.66 
                 D 
                 40.66 
                 D 
                 −19.58 
                 D 
                 0.5 
               
               
                 339 
                 D 
                 −44.53 
                 D 
                 35.79 
                 S 
                 −4.37 
                 D 
                 −4.37 
               
               
                 340 
                 D 
                 −49.4 
                 S 
                 51 
                 D 
                 −9.24 
                 D 
                 −9.24 
               
               
                 341 
                 D 
                 −54.27 
                 D 
                 46.13 
                 D 
                 −14.11 
                 S 
                 5.97 
               
               
                 342 
                 D 
                 −59.14 
                 D 
                 41.26 
                 D 
                 −18.98 
                 D 
                 1.1 
               
               
                 343 
                 D 
                 −64.01 
                 D 
                 36.39 
                 S 
                 −3.77 
                 D 
                 −3.77 
               
               
                 344 
                 D 
                 −68.88 
                 S 
                 51.6 
                 D 
                 −8.64 
                 D 
                 −8.64 
               
               
                 345 
                 S 
                 −53.67 
                 D 
                 46.73 
                 D 
                 −13.51 
                 S 
                 6.57 
               
               
                 346 
                 S 
                 −38.46 
                 D 
                 41.86 
                 D 
                 −18.38 
                 D 
                 1.7 
               
               
                 347 
                 S 
                 −23.25 
                 D 
                 36.99 
                 S 
                 −3.17 
                 D 
                 −3.17 
               
               
                 348 
                 S 
                 −8.04 
                 S 
                 52.2 
                 D 
                 −8.04 
                 D 
                 −8.04 
               
               
                 349 
                 S 
                 7.17 
                 D 
                 47.33 
                 D 
                 −12.91 
                 S 
                 7.17 
               
               
                 350 
                 S 
                 22.38 
                 D 
                 42.46 
                 D 
                 −17.78 
                 D 
                 2.3 
               
               
                 351 
                 S 
                 37.59 
                 D 
                 37.59 
                 S 
                 −2.57 
                 D 
                 −2.57 
               
               
                 352 
                 S 
                 52.8 
                 S 
                 52.8 
                 D 
                 −7.44 
                 D 
                 −7.44 
               
               
                 353 
                 D 
                 47.93 
                 D 
                 47.93 
                 D 
                 −12.31 
                 S 
                 7.77 
               
               
                 354 
                 D 
                 43.06 
                 D 
                 43.06 
                 D 
                 −17.18 
                 D 
                 2.9 
               
               
                 355 
                 D 
                 38.19 
                 D 
                 38.19 
                 S 
                 −1.97 
                 D 
                 −1.97 
               
               
                 356 
                 D 
                 33.32 
                 S 
                 53.4 
                 D 
                 −6.84 
                 D 
                 −6.84 
               
               
                 357 
                 D 
                 28.45 
                 D 
                 48.53 
                 D 
                 −11.71 
                 S 
                 8.37 
               
               
                 358 
                 D 
                 23.58 
                 D 
                 43.66 
                 D 
                 −16.58 
                 D 
                 3.5 
               
               
                 359 
                 D 
                 18.71 
                 D 
                 38.79 
                 S 
                 −1.37 
                 D 
                 −1.37 
               
               
                 360 
                 D 
                 13.84 
                 S 
                 54 
                 D 
                 −6.24 
                 D 
                 −6.24 
               
               
                 361 
                 D 
                 8.97 
                 D 
                 49.13 
                 D 
                 −11.11 
                 S 
                 8.97 
               
               
                 362 
                 D 
                 4.1 
                 D 
                 44.26 
                 D 
                 −15.98 
                 D 
                 4.1 
               
               
                 363 
                 D 
                 −0.77 
                 D 
                 39.39 
                 S 
                 −0.77 
                 D 
                 −0.77 
               
               
                 364 
                 D 
                 −5.64 
                 S 
                 54.6 
                 D 
                 −5.64 
                 D 
                 −5.64 
               
               
                 365 
                 D 
                 −10.51 
                 D 
                 49.73 
                 D 
                 −10.51 
                 D 
                 −10.51 
               
               
                 366 
                 D 
                 −15.38 
                 D 
                 44.86 
                 D 
                 −15.38 
                 S 
                 4.7 
               
               
                 367 
                 D 
                 −20.25 
                 D 
                 39.99 
                 D 
                 −20.25 
                 D 
                 −0.17 
               
               
                 368 
                 D 
                 −25.12 
                 S 
                 55.2 
                 S 
                 −5.04 
                 D 
                 −5.04 
               
               
                 369 
                 D 
                 −29.99 
                 D 
                 50.33 
                 D 
                 −9.91 
                 D 
                 −9.91 
               
               
                 370 
                 D 
                 −34.86 
                 D 
                 45.46 
                 D 
                 −14.78 
                 S 
                 5.3 
               
               
                 371 
                 D 
                 −39.73 
                 D 
                 40.59 
                 D 
                 −19.65 
                 D 
                 0.43 
               
               
                 372 
                 D 
                 −44.6 
                 S 
                 55.8 
                 S 
                 −4.44 
                 D 
                 −4.44 
               
               
                 373 
                 D 
                 −49.47 
                 D 
                 50.93 
                 D 
                 −9.31 
                 D 
                 −9.31 
               
               
                 374 
                 D 
                 −54.34 
                 D 
                 46.06 
                 D 
                 −14.18 
                 S 
                 5.9 
               
               
                 375 
                 D 
                 −59.21 
                 D 
                 41.19 
                 D 
                 −19.05 
                 D 
                 1.03 
               
               
                 376 
                 D 
                 −64.08 
                 S 
                 56.4 
                 S 
                 −3.84 
                 D 
                 −3.84 
               
               
                 377 
                 S 
                 −48.87 
                 D 
                 51.53 
                 D 
                 −8.71 
                 D 
                 −8.71 
               
               
                 378 
                 S 
                 −33.66 
                 D 
                 46.66 
                 D 
                 −13.58 
                 S 
                 6.5 
               
               
                 379 
                 S 
                 −18.45 
                 D 
                 41.79 
                 D 
                 −18.45 
                 D 
                 1.63 
               
               
                 380 
                 S 
                 −3.24 
                 S 
                 57 
                 S 
                 −3.24 
                 D 
                 −3.24 
               
               
                 381 
                 S 
                 11.97 
                 D 
                 52.13 
                 D 
                 −8.11 
                 D 
                 −8.11 
               
               
                 382 
                 S 
                 27.18 
                 D 
                 47.26 
                 D 
                 −12.98 
                 S 
                 7.1 
               
               
                 383 
                 S 
                 42.39 
                 D 
                 42.39 
                 D 
                 −17.85 
                 D 
                 2.23 
               
               
                 384 
                 S 
                 57.6 
                 S 
                 57.6 
                 S 
                 −2.64 
                 D 
                 −2.64 
               
               
                 385 
                 D 
                 52.73 
                 D 
                 52.73 
                 D 
                 −7.51 
                 D 
                 −7.51 
               
               
                 386 
                 D 
                 47.86 
                 D 
                 47.86 
                 D 
                 −12.38 
                 S 
                 7.7 
               
               
                 387 
                 D 
                 42.99 
                 D 
                 42.99 
                 D 
                 −17.25 
                 D 
                 2.83 
               
               
                 388 
                 D 
                 38.12 
                 S 
                 58.2 
                 S 
                 −2.04 
                 D 
                 −2.04 
               
               
                 389 
                 D 
                 33.25 
                 D 
                 53.33 
                 D 
                 −6.91 
                 D 
                 −6.91 
               
               
                 390 
                 D 
                 28.38 
                 D 
                 48.46 
                 D 
                 −11.78 
                 S 
                 8.3 
               
               
                 391 
                 D 
                 23.51 
                 D 
                 43.59 
                 D 
                 −16.65 
                 D 
                 3.43 
               
               
                 392 
                 D 
                 18.64 
                 S 
                 58.8 
                 S 
                 −1.44 
                 D 
                 −1.44 
               
               
                 393 
                 D 
                 13.77 
                 D 
                 53.93 
                 D 
                 −6.31 
                 D 
                 −6.31 
               
               
                 394 
                 D 
                 8.9 
                 D 
                 49.06 
                 D 
                 −11.18 
                 S 
                 8.9 
               
               
                 395 
                 D 
                 4.03 
                 D 
                 44.19 
                 D 
                 −16.05 
                 D 
                 4.03 
               
               
                 396 
                 D 
                 −0.84 
                 S 
                 59.4 
                 S 
                 −0.84 
                 D 
                 −0.84 
               
               
                 397 
                 D 
                 −5.71 
                 D 
                 54.53 
                 D 
                 −5.71 
                 D 
                 −5.71 
               
               
                 398 
                 D 
                 −10.58 
                 D 
                 49.66 
                 D 
                 −10.58 
                 D 
                 −10.58 
               
               
                 399 
                 D 
                 −15.45 
                 D 
                 44.79 
                 D 
                 −15.45 
                 S 
                 4.63 
               
               
                 400 
                 D 
                 −20.32 
                 S 
                 60 
                 D 
                 −20.32 
                 D 
                 −0.24 
               
               
                 401 
                 D 
                 −25.19 
                 D 
                 55.13 
                 S 
                 −5.11 
                 D 
                 −5.11 
               
               
                 402 
                 D 
                 −30.06 
                 D 
                 50.26 
                 D 
                 −9.98 
                 D 
                 −9.98 
               
               
                 403 
                 D 
                 −34.93 
                 D 
                 45.39 
                 D 
                 −14.85 
                 S 
                 5.23 
               
               
                 404 
                 D 
                 −39.8 
                 S 
                 60.6 
                 D 
                 −19.72 
                 D 
                 0.36 
               
               
                 405 
                 D 
                 −44.67 
                 D 
                 55.73 
                 S 
                 −4.51 
                 D 
                 −4.51 
               
               
                 406 
                 D 
                 −49.54 
                 D 
                 50.86 
                 D 
                 −9.38 
                 D 
                 −9.38 
               
               
                 407 
                 D 
                 −54.41 
                 D 
                 45.99 
                 D 
                 −14.25 
                 S 
                 5.83 
               
               
                 408 
                 D 
                 −59.28 
                 S 
                 61.2 
                 D 
                 −19.12 
                 D 
                 0.96 
               
               
                 409 
                 S 
                 −44.07 
                 D 
                 56.33 
                 S 
                 −3.91 
                 D 
                 −3.91 
               
               
                 410 
                 S 
                 −28.86 
                 D 
                 51.46 
                 D 
                 −8.78 
                 D 
                 −8.78 
               
               
                 411 
                 S 
                 −13.65 
                 D 
                 46.59 
                 D 
                 −13.65 
                 S 
                 6.43 
               
               
                 412 
                 S 
                 1.56 
                 S 
                 61.8 
                 D 
                 −18.52 
                 D 
                 1.56 
               
               
                 413 
                 S 
                 16.77 
                 D 
                 56.93 
                 S 
                 −3.31 
                 D 
                 −3.31 
               
               
                 414 
                 S 
                 31.98 
                 D 
                 52.06 
                 D 
                 −8.18 
                 D 
                 −8.18 
               
               
                 415 
                 S 
                 47.19 
                 D 
                 47.19 
                 D 
                 −13.05 
                 S 
                 7.03 
               
               
                 416 
                 S 
                 62.4 
                 S 
                 62.4 
                 D 
                 −17.92 
                 D 
                 2.16 
               
               
                 417 
                 D 
                 57.53 
                 D 
                 57.53 
                 S 
                 −2.71 
                 D 
                 −2.71 
               
               
                 418 
                 D 
                 52.66 
                 D 
                 52.66 
                 D 
                 −7.58 
                 D 
                 −7.58 
               
               
                 419 
                 D 
                 47.79 
                 D 
                 47.79 
                 D 
                 −12.45 
                 S 
                 7.63 
               
               
                 420 
                 D 
                 42.92 
                 S 
                 63 
                 D 
                 −17.32 
                 D 
                 2.76 
               
               
                 421 
                 D 
                 38.05 
                 D 
                 58.13 
                 S 
                 −2.11 
                 D 
                 −2.11 
               
               
                 422 
                 D 
                 33.18 
                 D 
                 53.26 
                 D 
                 −6.98 
                 D 
                 −6.98 
               
               
                 423 
                 D 
                 28.31 
                 D 
                 48.39 
                 D 
                 −11.85 
                 S 
                 8.23 
               
               
                 424 
                 D 
                 23.44 
                 S 
                 63.6 
                 D 
                 −16.72 
                 D 
                 3.36 
               
               
                 425 
                 D 
                 18.57 
                 D 
                 58.73 
                 S 
                 −1.51 
                 D 
                 −1.51 
               
               
                 426 
                 D 
                 13.7 
                 D 
                 53.86 
                 D 
                 −6.38 
                 D 
                 −6.38 
               
               
                 427 
                 D 
                 8.83 
                 D 
                 48.99 
                 D 
                 −11.25 
                 D 
                 −11.25 
               
               
                 428 
                 D 
                 3.96 
                 S 
                 64.2 
                 D 
                 −16.12 
                 S 
                 3.96 
               
               
                 429 
                 D 
                 −0.91 
                 D 
                 59.33 
                 D 
                 −20.99 
                 D 
                 −0.91 
               
               
                 430 
                 D 
                 −5.78 
                 D 
                 54.46 
                 S 
                 −5.78 
                 D 
                 −5.78 
               
               
                 431 
                 D 
                 −10.65 
                 D 
                 49.59 
                 D 
                 −10.65 
                 D 
                 −10.65 
               
               
                 432 
                 D 
                 −15.52 
                 S 
                 64.8 
                 D 
                 −15.52 
                 S 
                 4.56 
               
               
                 433 
                 D 
                 −20.39 
                 D 
                 59.93 
                 D 
                 −20.39 
                 D 
                 −0.31 
               
               
                 434 
                 D 
                 −25.26 
                 D 
                 55.06 
                 S 
                 −5.18 
                 D 
                 −5.18 
               
               
                 435 
                 D 
                 −30.13 
                 D 
                 50.19 
                 D 
                 −10.05 
                 D 
                 −10.05 
               
               
                 436 
                 D 
                 −35 
                 S 
                 65.4 
                 D 
                 −14.92 
                 S 
                 5.16 
               
               
                 437 
                 D 
                 −39.87 
                 D 
                 60.53 
                 D 
                 −19.79 
                 D 
                 0.29 
               
               
                 438 
                 D 
                 −44.74 
                 D 
                 55.66 
                 S 
                 −4.58 
                 D 
                 −4.58 
               
               
                 439 
                 D 
                 −49.61 
                 D 
                 50.79 
                 D 
                 −9.45 
                 D 
                 −9.45 
               
               
                 440 
                 D 
                 −54.48 
                 S 
                 66 
                 D 
                 −14.32 
                 S 
                 5.76 
               
               
                 441 
                 S 
                 −39.27 
                 D 
                 61.13 
                 D 
                 −19.19 
                 D 
                 0.89 
               
               
                 442 
                 S 
                 −24.06 
                 D 
                 56.26 
                 S 
                 −3.98 
                 D 
                 −3.98 
               
               
                 443 
                 S 
                 −8.85 
                 D 
                 51.39 
                 D 
                 −8.85 
                 D 
                 −8.85 
               
               
                 444 
                 S 
                 6.36 
                 S 
                 66.6 
                 D 
                 −13.72 
                 S 
                 6.36 
               
               
                 445 
                 S 
                 21.57 
                 D 
                 61.73 
                 D 
                 −18.59 
                 D 
                 1.49 
               
               
                 446 
                 S 
                 36.78 
                 D 
                 56.86 
                 S 
                 −3.38 
                 D 
                 −3.38 
               
               
                 447 
                 S 
                 51.99 
                 D 
                 51.99 
                 D 
                 −8.25 
                 D 
                 −8.25 
               
               
                 448 
                 S 
                 67.2 
                 S 
                 67.2 
                 D 
                 −13.12 
                 S 
                 6.96 
               
               
                 449 
                 D 
                 62.33 
                 D 
                 62.33 
                 D 
                 −17.99 
                 D 
                 2.09 
               
               
                 450 
                 D 
                 57.46 
                 D 
                 57.46 
                 S 
                 −2.78 
                 D 
                 −2.78 
               
               
                 451 
                 D 
                 52.59 
                 D 
                 52.59 
                 D 
                 −7.65 
                 D 
                 −7.65 
               
               
                 452 
                 D 
                 47.72 
                 S 
                 67.8 
                 D 
                 −12.52 
                 S 
                 7.56 
               
               
                 453 
                 D 
                 42.85 
                 D 
                 62.93 
                 D 
                 −17.39 
                 D 
                 2.69 
               
               
                 454 
                 D 
                 37.98 
                 D 
                 58.06 
                 S 
                 −2.18 
                 D 
                 −2.18 
               
               
                 455 
                 D 
                 33.11 
                 D 
                 53.19 
                 D 
                 −7.05 
                 D 
                 −7.05 
               
               
                 456 
                 D 
                 28.24 
                 S 
                 68.4 
                 D 
                 −11.92 
                 D 
                 −11.92 
               
               
                 457 
                 D 
                 23.37 
                 D 
                 63.53 
                 D 
                 −16.79 
                 S 
                 3.29 
               
               
                 458 
                 D 
                 18.5 
                 D 
                 58.66 
                 D 
                 −21.66 
                 D 
                 −1.58 
               
               
                 459 
                 D 
                 13.63 
                 D 
                 53.79 
                 S 
                 −6.45 
                 D 
                 −6.45 
               
               
                 460 
                 D 
                 8.76 
                 S 
                 69 
                 D 
                 −11.32 
                 D 
                 −11.32 
               
               
                 461 
                 D 
                 3.89 
                 D 
                 64.13 
                 D 
                 −16.19 
                 S 
                 3.89 
               
               
                 462 
                 D 
                 −0.98 
                 D 
                 59.26 
                 D 
                 −21.06 
                 D 
                 −0.98 
               
               
                 463 
                 D 
                 −5.85 
                 D 
                 54.39 
                 S 
                 −5.85 
                 D 
                 −5.85 
               
               
                 464 
                 D 
                 −10.72 
                 S 
                 69.6 
                 D 
                 −10.72 
                 D 
                 −10.72 
               
               
                 465 
                 D 
                 −15.59 
                 D 
                 64.73 
                 D 
                 −15.59 
                 S 
                 4.49 
               
               
                 466 
                 D 
                 −20.46 
                 D 
                 59.86 
                 D 
                 −20.46 
                 D 
                 −0.38 
               
               
                 467 
                 D 
                 −25.33 
                 D 
                 54.99 
                 S 
                 −5.25 
                 D 
                 −5.25 
               
               
                 468 
                 D 
                 −30.2 
                 S 
                 70.2 
                 D 
                 −10.12 
                 D 
                 −10.12 
               
               
                 469 
                 D 
                 −35.07 
                 D 
                 65.33 
                 D 
                 −14.99 
                 S 
                 5.09 
               
               
                 470 
                 D 
                 −39.94 
                 D 
                 60.46 
                 D 
                 −19.86 
                 D 
                 0.22 
               
               
                 471 
                 D 
                 −44.81 
                 D 
                 55.59 
                 S 
                 −4.65 
                 D 
                 −4.65 
               
               
                 472 
                 D 
                 −49.68 
                 S 
                 70.8 
                 D 
                 −9.52 
                 D 
                 −9.52 
               
               
                 473 
                 S 
                 −34.47 
                 D 
                 65.93 
                 D 
                 −14.39 
                 S 
                 5.69 
               
               
                 474 
                 S 
                 −19.26 
                 D 
                 61.06 
                 D 
                 −19.26 
                 D 
                 0.82 
               
               
                 475 
                 s 
                 −4.05 
                 D 
                 56.19 
                 S 
                 −4.05 
                 D 
                 −4.05 
               
               
                 476 
                 s 
                 11.16 
                 S 
                 71.4 
                 D 
                 −8.92 
                 D 
                 −8.92 
               
               
                 477 
                 s 
                 26.37 
                 D 
                 66.53 
                 D 
                 −13.79 
                 S 
                 6.29 
               
               
                 478 
                 s 
                 41.58 
                 D 
                 61.66 
                 D 
                 −18.66 
                 D 
                 1.42 
               
               
                 479 
                 s 
                 56.79 
                 D 
                 56.79 
                 S 
                 −3.45 
                 D 
                 −3.45 
               
               
                 480 
                 s 
                 72 
                 S 
                 72 
                 D 
                 −8.32 
                 D 
                 −8.32 
               
               
                 481 
                 D 
                 67.13 
                 D 
                 67.13 
                 D 
                 −13.19 
                 S 
                 6.89 
               
               
                 482 
                 D 
                 62.26 
                 D 
                 62.26 
                 D 
                 −18.06 
                 D 
                 2.02 
               
               
                 483 
                 D 
                 57.39 
                 D 
                 57.39 
                 S 
                 −2.85 
                 D 
                 −2.85 
               
               
                 484 
                 D 
                 52.52 
                 S 
                 72.6 
                 D 
                 −7.72 
                 D 
                 −7.72 
               
               
                 485 
                 D 
                 47.65 
                 D 
                 67.73 
                 D 
                 −12.59 
                 S 
                 7.49 
               
               
                 486 
                 D 
                 42.78 
                 D 
                 62.86 
                 D 
                 −17.46 
                 D 
                 2.62 
               
               
                 487 
                 D 
                 37.91 
                 D 
                 57.99 
                 S 
                 −2.25 
                 D 
                 −2.25 
               
               
                 488 
                 D 
                 33.04 
                 S 
                 73.2 
                 D 
                 −7.12 
                 D 
                 −7.12 
               
               
                 489 
                 D 
                 28.17 
                 D 
                 68.33 
                 D 
                 −11.99 
                 D 
                 −11.99 
               
               
                 490 
                 D 
                 23.3 
                 D 
                 63.46 
                 D 
                 −16.86 
                 S 
                 3.22 
               
               
                 491 
                 D 
                 18.43 
                 D 
                 58.59 
                 D 
                 −21.73 
                 D 
                 −1.65 
               
               
                 492 
                 D 
                 13.56 
                 S 
                 73.8 
                 S 
                 −6.52 
                 D 
                 −6.52 
               
               
                 493 
                 D 
                 8.69 
                 D 
                 68.93 
                 D 
                 −11.39 
                 D 
                 −11.39 
               
               
                 494 
                 D 
                 3.82 
                 D 
                 64.06 
                 D 
                 −16.26 
                 S 
                 3.82 
               
               
                 495 
                 D 
                 −1.05 
                 D 
                 59.19 
                 D 
                 −21.13 
                 D 
                 −1.05 
               
               
                 496 
                 D 
                 −5.92 
                 S 
                 74.4 
                 S 
                 −5.92 
                 D 
                 −5.92 
               
               
                 497 
                 D 
                 −10.79 
                 D 
                 69.53 
                 D 
                 −10.79 
                 D 
                 −10.79 
               
               
                 498 
                 D 
                 −15.66 
                 D 
                 64.66 
                 D 
                 −15.66 
                 S 
                 4.42 
               
               
                 499 
                 D 
                 −20.53 
                 D 
                 59.79 
                 D 
                 −20.53 
                 D 
                 −0.45 
               
               
                 500 
                 D 
                 −25.4 
                 S 
                 75 
                 S 
                 −5.32 
                 D 
                 −5.32 
               
               
                   
               
            
           
         
       
     
     Table 2 illustrates statistics for each of Cases 1, 2, 3, and 4. In particular, Table 2 lists, for each case, the minimum total voltage disturbance value, the maximum total voltage disturbance value, the difference between these two values, and the average total voltage disturbance value (in mV). It should be appreciated that Case 4, in this example, provides an average total voltage disturbance value that is closest 0. In other words, across all the options of how many current source unit cells  114  are turned on, the ordering of Case 4 may provide a total voltage disturbance at V bias  that is, on average, closest to 0.  FIG. 14  illustrates the information in Table 1 in graph form. Data set  1401  represents the total voltage disturbance as a function of the number of cells that are turned on for case 1. Data set  1402  represents the total voltage disturbance as a function of the number of cells that are turned on for case 2. Data set  1403  represents the total voltage disturbance as a function of the number of cells that are turned on for case 3. Data set  1404  represents the total voltage disturbance as a function of the number of cells that are turned on for case 4. In this plot, the total voltage disturbance is expressed in millivolts (mV). As shown in this figure, cases 3 and 4 are characterized by mean values that are relatively close to 0, especially when compared to cases 1 and 2. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Statistics for the four cases illustrated in Table 1. 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                 Min Value 
                 Max Value 
                 Max-Min 
                 Average 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Case 1 
                 −116.88 
                 72 
                 188.88 
                 −22.3638 
               
               
                   
                 Case 2 
                 −14.61 
                 75 
                 89.61 
                 30.045 
               
               
                   
                 Case 3 
                 −21.73 
                 4.2 
                 25.93 
                 −8.74956 
               
               
                   
                 Case 4 
                 −11.99 
                 13.94 
                 25.93 
                 0.96916 
               
               
                   
                   
               
            
           
         
       
     
     In some embodiments, the PLL controller  111  may not include the fine control circuitry  115 , and the PLL controller  111  may only control turning on and off of the current source unit cells  114  or  714  in blocks. In some embodiments, the PLL controller  111  may not include the coarse control circuitry  113 , and the PLL controller  111  may only control turning on and off of the current source unit cells  114  or  714  with single current source unit cell resolution. 
     In some embodiments, a method includes using an ultrasound device having any of the PLLs (e.g., the PLL  102  or the PLL  702 ) described above. As described above, the PLL may include a DCO (e.g., the DCO  110  or the DCO  710 ) having current source unit cells with drain switch current source unit cells with source switch. Using the ultrasound device may include switching on a certain number of the plurality of current source unit cells with drain switch and a certain number of the plurality of current source unit cells with source switch. Further description of PLLs, DCOs, various example topologies for the current source unit cells, and various methods for switching on the current source unit cells may be found above. 
       FIG. 15  illustrates a functional block diagram of an exemplary ultrasound-on-chip device  3300 , in accordance with certain embodiments described herein.  FIG. 15  also illustrates a printed circuit board (PCB)  3378 . The ultrasound-on-chip device  3300  includes a first device  3302  and a second device  3306 . The first device  3302  and the second device  3306  may each be dies that are packaged together to form the ultrasound-on-chip device  3300 . The first device  3302  and the second device  3306  may be application-specific integrated circuits (ASICs). The first device  3302  includes a plurality of elements  3358  (which may also be considered pixels). While only four elements  3358  are shown in  FIG. 15 , it should be appreciated that many more elements  3358  may be included, such as hundreds, thousands, or tens of thousands of elements. Each of the elements  3358  includes an ultrasonic transducer  3360 , a pulser  3364 , a receive switch  3362 , an analog receive circuitry  3310  block, and an analog-to-digital converter (ADC)  3312 . The first device  3302  includes the ultrasonic transducers  3360 , the pulsers  3364 , the receive switches  3362 , the analog receive circuitry  3310 , the ADCs  3312 , SERDES transmit circuitry  3352 , power circuitry  3348 , clocking circuitry  3324 , sequencing circuitry  3328 , control circuitry  3326 , and communication circuitry  3322 . The second device  3306  includes SERDES receive circuitry  3354 , digital receive circuitry  3376 , power circuitry  3372 , clocking circuitry  3332 , sequencing circuitry  3336 , control circuitry  3334 , communication circuitry  3330 , memory circuitry  3340 , peripheral management circuitry  3338 , monitoring circuitry  3374 , and processing circuitry  3356 . A communication link  3350  electrically connects the SERDES transmit circuitry  3352  in the first device  3302  to the SERDES receive circuity  3354  in the second device  3306 . A communication link  3370  electrically connects the communication circuitry  3322  in the first device  3302  to the communication circuitry  3330  in the second device  3306 . A communication link  3382  electrically connects the communication circuitry  3322  in the first device  3302  to the PCB  3378 . A communication link  3384  electrically connects the communication circuitry  3330  in the second device  3306  to the PCB  3378 . 
     A pulser  3364  may be configured to output a driving signal to an ultrasonic transducer  3360 . The pulser  3364  may receive a waveform from a waveform generator (not shown) and be configured to output a driving signal corresponding to the received waveform. When the pulser  3364  is driving the ultrasonic transducer  3360  (the “transmit phase”), the receive switch  3362  may be open such that the driving signal is not applied to receive circuitry (e.g., the analog receive circuitry  3310 ). 
     The ultrasonic transducer  3360  may be configured to emit pulsed ultrasonic signals into a subject, such as a patient, in response to the driving signal received from the pulser  3364 . The pulsed ultrasonic signals may be back-scattered from structures in the body, such as blood cells or muscular tissue, to produce echoes that return to the ultrasonic transducer  3360 . The ultrasonic transducer  3360  may be configured to convert these echoes into electrical signals. When the ultrasonic transducer  3360  is receiving the echoes (the “receive phase”), the receive switch  3362  may be closed such that the ultrasonic transducer  3360  may transmit the electrical signals representing the received echoes through the receive switch  3362  to the analog receive circuitry  3310 . Example ultrasonic transducers  3360  include capacitive micromachined ultrasonic transducers (CMUTs) and piezoelectric micromachined ultrasonic transducers (PMUTs). For example, CMUTs may include cavities formed in a substrate with a membrane/membranes overlying the cavity. The ultrasonic transducers may be arranged in an array (e.g., one-dimensional or two-dimensional). 
     The analog receive circuitry  3310  may include, for example, one or more analog amplifiers, one or more analog filters, analog beamforming circuitry, analog dechirp circuitry, analog quadrature demodulation (AQDM) circuitry, analog time delay circuitry, analog phase shifter circuitry, analog summing circuitry, analog time gain compensation circuitry, and/or analog averaging circuitry. The analog output of the analog receive circuitry  3310  is outputted to the ADC  3312  for conversion to a digital signal. The digital output of the ADC  3312  is outputted to the SERDES transmit circuitry  3352 . 
     The SERDES transmit circuitry  3352  may be configured to convert parallel digital output of the ADC  3312  to a serial digital stream and to output the serial digital stream at a high-speed (e.g., 2-5 gigabits/second or more) over the communication link  3350 . The SERDES receive circuitry  3354  may be configured to convert the serial digital stream received from the communication link  3350  to a parallel digital output and to output this parallel digital output to the digital receive circuitry  3376 . 
     In the ultrasound-on-chip device  3300 , one block of SERDES transmit circuitry  3352  receives data from multiple ADC&#39;s  3312  and is electrically coupled, through the communication link  3350 , to one block of SERDES receive circuitry  3354  that is coupled to the digital receive circuitry  3376 . There may be multiple instances of SERDES transmit circuitry  3352 , communication link  3350 , and SERDES receive circuitry  3354 , each receiving data from multiple ADC&#39;s  3312 . In some embodiments, there may be one instance of SERDES transmit circuitry  3352 , communication link  3350 , and SERDES receive circuitry  3354  per ADC  3312  and/or per ultrasonic transducer  3360 , or more generally, per element  3358 . In some embodiments, there may be approximately equal to or between 1-100 parallel instances of SERDES transmit circuitry  3352 , communication link  3350 , and SERDES receive circuitry  3354 . In some embodiments, there may be approximately equal to or between 1-10,000 parallel instances of SERDES transmit circuitry  3352 , communication link  3350 , and SERDES receive circuitry  3354 . The data offload rate of all the parallel instances of SERDES transmit circuitry  3352 , communication link  3350 , and SERDES receive circuitry  3354  may make the ultrasound-on-chip device  3300  acoustically limited, meaning that it may not be necessary to insert undesired time between collection of frames of ultrasound data to offload data from the ultrasound-on-chip device  3300 . The data offload rate may facilitate high pulse repetition intervals (e.g., greater than or equal to approximately 10 kHz). 
     In some embodiments, the SERDES receive circuitry  3354  may include a mesochronous receiver. In some embodiments, the SERDES receive circuitry  3354  may include a digital PLL, a digital clock and data recovery circuit, and an equalizer. In some embodiments, the PLL of the SERDES receive circuitry  3354  may be implemented using any of the PLL described above. Thus, the PLL may use fast on/off techniques that allow the PLL to power down and conserve power when the ultrasound-on-chip device  3300  is not generating data, and power up to full operating within an acceptably fast period of time when the ultrasound-on-chip device  3300  begins to generate data again. At the same time, the PLL may be configured to prevent large disturbances that may otherwise cause an increase in the settling time of the voltage at a bias node. 
     The digital receive circuitry  3376  may include, for example, one or more digital filters, digital beamforming circuitry, digital quadrature demodulation (DQDM) circuitry, averaging circuitry, digital dechirp circuitry, digital time delay circuitry, digital phase shifter circuitry, digital summing circuitry, digital multiplying circuitry, requantization circuitry, waveform removal circuitry, image formation circuitry, backend processing circuitry and/or one or more output buffers. The image formation circuitry in the digital receive circuitry  3376  may be configured to perform apodization, back projection and/or fast hierarchy back projection, interpolation range migration (e.g., Stolt interpolation) or other Fourier resampling techniques, dynamic focusing techniques, delay and sum techniques, tomographic reconstruction techniques, Doppler calculation, frequency and spatial compounding, and/or low and high-pass filtering, etc. 
     Referring to the first device  3302 , the communication circuitry  3322  in the first device  3302  may be configured to provide communication between the first device  3302  and the second device  3306  over the communication link  3370  (or more than one communication links  3370 ). The communication circuitry  3322  may facilitate communication of signals from any circuitry on the first device  3302  to the second device  3306  and/or communication of signals from any circuitry on the second device  3306  to the first device  3302  (aside from communication facilitated by the SERDES transmit circuitry  3352 , the communication link  3350 , and the SERDES receive circuitry  3354 ). 
     The communication circuitry  3322  in the first device  3302  may also be configured to provide communication between the first device  3302  and the PCB  3378  over the communication link  3382  (or more than one communication links  3382 ). The communication circuitry  3322  may facilitate communication of signals from any circuitry on the first device  3302  to the PCB  3378  and/or communication of signals from any circuitry on the PCB  3378  to the first device  3302 . For example, the PCB  3378  may provide control signals to the first device  3302  through the communication link  3382  and the communication circuitry  3322  that may then be used by the control circuitry  3326 . 
     The clocking circuitry  3324  in the first device  3302  may be configured to generate some or all of the clocks used in the first device  3302  and/or the second device  3306 . In some embodiments, the clocking circuitry  3324  may receive a high-speed clock (e.g., a 1.5625 GHz or a 2.5 GHz clock) from an external source that the clocking circuitry  3324  may feed to various circuit components of the ultrasound-on-chip device  3300 . In some embodiments, the clocking circuitry  3324  may divide and/or multiply the received high-speed clock to produce clocks of different frequencies (e.g., 20 MHz, 40 MHz, 100 MHz, or 200 MHz) that the clocking circuitry  3324  may feed to various components of the ultrasound-on-chip device  3300 . In some embodiments, the clocking circuitry  3324  may separately receive two or more clocks of different frequencies, such as the frequencies described above. 
     The control circuitry  3326  in the first device  3302  may be configured to control various circuit components in the first device  3302 . For example, the control circuitry  3326  may control and/or parameterize the pulsers  3364 , the receive switches  3362 , the analog receive circuitry  3310 , the ADCs  3312 , the SERDES transmit circuitry  3352 , the power circuitry  3348 , the communication circuitry  3322 , the clocking circuitry  3324 , the sequencing circuitry  3328 , digital waveform generators, delay meshes, and/or time-gain compensation circuitry (the latter three of which are not shown in  FIG. 15 ). The control circuitry  3326  may also be configured to control any circuitry on the second device  3306 . 
     The sequencing circuitry  3328  in the first device  3302  may be configured to coordinate various circuit components on the first device  3302  that may or may not be digitally parameterized. In some embodiments, the sequencing circuitry  3328  may control the timing and ordering of parameter changes in the first device  3302  and/or the second device  3306 , control triggering of transmit and receive events, and control data flow (e.g., from the first device  3302  to the second device  3306 ). In some embodiments, the sequencing circuitry  3328  may control execution of an imaging sequence which may be specific to the selected imaging mode, preset, and user settings. In some embodiments, the sequencing circuitry  3328  in the first device  3302  may be configured as a master sequencer that triggers events on sequencing circuitry  3336  in the second device  3306  that is configured as a slave sequencer and has been digitally parameterized. In some embodiments, the sequencing circuitry  3336  in the second device  3306  is configured as a master sequencer that triggers events on the sequencing circuitry  3328  in the first device  3302  that is configured as a slave sequencer and has been digitally parameterized. In some embodiments, the sequencing circuitry  3328  in the first device  3302  is configured to control parameterized circuit components on both the first device  3302  and the second device  3306 . In some embodiments, the sequencing circuitry  3328  in the first device  3302  and the sequencing circuitry  3336  in the second device  3306  may operate in synchronization by using a clock derived from the same source (e.g., provided by the clocking circuitry). 
     The power circuitry  3348  in the first device  3302  may include low dropout regulators, switching power supplies, and/or DC-DC converters to supply the first device  3302  and/or the second device  3306 . In some embodiments, the power circuitry  3348  may include multi-level pulsers and/or charge recycling circuitry. 
     The second device  3306  additionally includes communication circuitry  3330 , clocking circuitry  3332 , control circuitry  3334 , sequencing circuitry  3336 , peripheral management circuitry  3338 , memory circuitry  3340 , power circuitry  3372 , processing circuitry  3356 , and monitoring circuitry  3374 . The communication circuitry  3330  in the second device  3306  may be configured to provide communication between the second device  3306  and the first device  3302  over the communication link  3370  (or more than one communication links  3370 ). The communication circuitry  3330  may facilitate communication of signals from any circuitry on the second device  3306  to the first device  3302  and/or communication of signals from any circuitry on the first device  3302  to the second device  3306 . 
     The communication circuitry  3330  in the second device  3306  may also be configured to provide communication between the second device  3306  and the PCB  3378  over the communication link  3384  (or more than one communication links  3384 ). The communication circuitry  3330  may facilitate communication of signals from any circuitry on the second device  3306  to the PCB  3378  and/or communication of signals from any circuitry on the PCB  3378  to the second device  3306 . For example, the PCB  3378  may provide control signals to the second device  3306  through the communication link  3384  and the communication circuitry  3330  that may then be used by the control circuitry  3334 . 
     The clocking circuitry  3332  in the second device  3306  may be configured to generate some or all of the clocks used in the second device  3306  and/or the first device  3302 . In some embodiments, the clocking circuitry  3332  may receive a high-speed clock (e.g., a 1.5625 GHz or a 2.5 GHz clock) that the clocking circuitry  3332  may feed to various circuit components of the ultrasound-on-chip device  3300 . In some embodiments, the clocking circuitry  3332  may divide and/or multiply the received high-speed clock to produce clocks of different frequencies (e.g., 20 MHz, 40 MHz, 100 MHz, or 200 MHz) that the clocking circuitry  3332  may feed to various components. In some embodiments, the clocking circuitry  3332  may separately receive two or more clocks of different frequencies, such as the frequencies described above. 
     The control circuitry  3334  in the second device  3306  may be configured to control various circuit components in the second device  3306 . For example, the control circuitry  3334  may control and/or parameterize the SERDES receive circuitry  3354 , the digital receive circuitry  3376 , the communication circuitry  3330 , the clocking circuitry  3332 , the sequencing circuitry  3336 , the peripheral management circuitry  3338 , the memory circuitry  3340 , the power circuitry  3372 , and the processing circuitry  3356 . The control circuitry  3334  may also be configured to control any circuitry on the first device  3302 . 
     The sequencing circuitry  3336  in the second device  3306  may be configured to coordinate various circuit components on the second device  3306  that may or may not be digitally parameterized. In some embodiments, the sequencing circuitry  3336  in the second device  3306  is configured as a master sequencer that triggers events on the sequencing circuitry  3328  in the first device  3302  that has been digitally parameterized. In some embodiments, the sequencing circuitry  3328  in the first device  3302  is configured as a master sequencer that triggers events on the sequencing circuitry  3336  in the first device  3302  that is configured as a slave sequencer and has been digitally parameterized. In some embodiments, the sequencing circuitry  3336  in the second device  3306  is configured to control parameterized circuit components on both the first device  3302  and the second device  3306 . In some embodiments, the sequencing circuitry  3336  in the second device  3306  and the sequencing circuitry  3328  in the first device  3302  may operate in synchronization by using a clock derived from the same source (e.g., provided by the clocking circuitry). 
     The peripheral management circuitry  3338  may be configured to generate a high-speed serial output data stream. For example, the peripheral management circuitry  3338  may be a Universal Serial Bus (USB) 2.0, 3.0, or 3.1 module. The peripheral management circuitry  3338  may additionally or alternatively be configured to allow an external microprocessor to control various circuit components of the ultrasound-on-chip device  3300  over a USB connection. As another example, the peripheral management circuitry  3338  may include a WiFi module or a module for controlling another type of peripheral. In some embodiments, this high-speed serial output data stream may be outputted to the PCB  3378 . 
     The memory circuitry  3340  may be configured to buffer and/or store digitized image data (e.g., image data produced by imaging formation circuitry and/or other circuitry in the digital receive circuitry  3376 ). For example, the memory circuitry  3340  may be configured to enable the ultrasound-on-chip device  3300  to retrieve image data in the absence of a wireless connection to a remote server storing the image data. Furthermore, when a wireless connection to a remote server is available, the memory circuitry  3340  may also be configured to provide support for wireless connectivity conditions such as lossy channels, intermittent connectivity, and lower data rates, for example. In addition to storing digitized image data, the memory circuitry  3340  may also be configured to store timing and control parameters for synchronizing and coordinating operation of elements in the ultrasound-on-chip device  3300 . The power circuitry  3372  may include power supply amplifiers for supplying power to the second device  3306 . 
     The processing circuitry  3356 , which may be in the form of one or more embedded processors, may be configured to perform processing functions. In some embodiments, the processing circuitry  3356  may be configured to perform sequencing functions, either for the first device  3302  or for the second device  3306 . For example, the processing circuitry  3356  may control the timing and ordering of parameter changes in the first device  3302  and/or the second device  3306 , control triggering of transmit and receive events, and/or control data flow (e.g., from the first device  3302  to the second device  3306 ). In some embodiments, the processing circuitry  3356  may control execution of an imaging sequence which may be specific to the selected imaging mode, preset, and user settings. In some embodiments, the processing circuitry  3356  may perform external system control, such as controlling the peripheral management circuitry  3338 , the processing circuitry  3356 , controlling power sequencing (e.g., for the power circuitry  3348  and/or the power circuitry  3372 ), and interfacing with the monitoring circuitry  3374 . In some embodiments, the processing circuitry  3356  may perform internal system control, such as configuring data flow within the chip (e.g., from the first device  3302  to the second device  3306 ), calculating or controlling the calculation of processing and image formation parameters (e.g., for image formation circuitry), controlling on chip clocking (e.g., for the clocking circuitry  3324  and/or the clocking circuitry  3332 ), and/or controlling power (e.g., for the power circuitry  3348  and/or the power circuitry  3372 ). The processing circuitry  3356  may be configured to perform functions described above as being performed by other components of the ultrasound-on-chip device  3300 , and in some embodiments certain components described herein may be absent if their functions are performed by the processing circuitry  3356 . 
     The monitoring circuitry  3374  may include, but is not limited to, temperature monitoring circuitry (e.g., thermistors), power measurement circuitry (e.g., voltage and current sensors), nine-axis motion circuitry (e.g., gyroscopes, accelerometers, compasses), battery monitoring circuitry (e.g., coulomb counters), and/or circuitry checking for status or exception conditions of other on-board circuits (e.g., power controllers, protection circuitry, etc.). 
     It should be understood that there may be many more instances of each component shown in  FIG. 15 . For example, there may be hundreds, thousands, or tens of thousands of ultrasonic transducers  3360 , pulsers  3364 , receive switches  3362 , analog receive circuitry  3310  blocks, SERDES transmit circuitry  3352  blocks, SERDES receive circuitry  3354  blocks, and/or digital receive circuitry  3376  blocks. Additionally, it should be understood that certain components shown in  FIG. 15  may receive signals from more components than shown or transmit signals to more components than shown (e.g., in a multiplexed fashion, or after averaging). For example, a given pulser  3364  may output signals to one or more ultrasonic transducers  3360 , a given receive switch  3362  may receive signals from one or more ultrasonic transducers  3360 , a given block of analog receive circuitry  3310  may receive signals from one or more receive switches  3362 , a given ADC  3312  may receive signals from one or more blocks of analog receive circuitry  3310 , a given block of SERDES transmit circuitry  3352  may receive signals from one or more ADCs  3312 . In some embodiments, a given ultrasound element may have an ultrasonic transducer  3360  and a dedicated pulser  3364 , receive switch  3362 , analog receive circuitry  3310  block, ADC  3312 , and/or SERDES transmit circuitry  3352  block. It should also be understood that certain embodiments of an ultrasound-on-chip device may have more or fewer components than shown in  FIG. 15 . 
     According to an aspect of the present application, an ultrasound device is provided, comprising a phase-locked loop (PLL) comprising a digitally-controlled oscillator (DCO) comprising a plurality of current source unit cells with respective drain switches and a plurality of current source unit cells with respective source switches. 
     In some embodiments, the plurality of current source unit cells with respective drain switches have a first circuit topology, the plurality of current source unit cells with respective source switches have a second circuit topology, and the first and second circuit topologies are different. 
     In some embodiments, the PLL is configured to use a fast switching technique that allows the PLL to power down when the ultrasound device is not generating data and to power up within 1 microsecond from when the ultrasound device begins to generate data again 
     In some embodiments, switching on one of the plurality of current source unit cells with respective drain switches causes a voltage transition at an internal node of the current source unit cell with respective drain switches proceeding in a first voltage direction, switching on of the plurality of current source unit cells with respective source switches causes a voltage transition at an internal node of the current source unit cell with respective source switches proceeding in a second voltage direction, and the first and second voltage directions are opposite. 
     In some embodiments, each of the plurality of current source unit cells with respective drain switches comprises a switch, and a current source wherein the current source comprises a first terminal and a second terminal and the switch is coupled to the first terminal of the current source and each of the plurality of current source unit cells with respective source switches comprises the switch and the current source wherein the switch is coupled to the second terminal of the current source. 
     In some embodiments, the current source comprises a single transistor, the first terminal comprises a drain of the transistor, and the second terminal comprises a source of the transistor. 
     In some embodiments, the current source comprises a cascode current source that comprises multiple transistors, the first terminal comprises a drain of one of the multiple transistors, and the second terminal comprises a source of the one of the multiple transistors. 
     In some embodiments, the switch comprises a single transistor. 
     In some embodiments, the switch comprises a transmission gate. 
     In some embodiments, the current source comprises at least one transistor having a gate terminal, and the gate terminal is coupled to an output of a resistor-capacitor (RC) filter. 
     In some embodiments, the RC filter is coupled to an output terminal of bias generation circuitry. 
     In some embodiments, the switch comprises at least one transistor having a gate terminal, the PLL comprises a decoder having a plurality of output terminals; and the gate terminal of the transistor is coupled to one of the plurality of output terminals of the decoder. 
     In some embodiments, the DCO comprises a ring oscillator and each of the plurality of current source unit cells with respective drain switches and each of the plurality of current source unit cells with respective source switches is couplable to the ring oscillator. 
     In some embodiments, the ring oscillator is configured to generate a clock signal having a frequency that depends on an amount of current that the ring oscillator receives from the plurality of current source unit cells with respective drain switches and the plurality of current source unit cells with respective source switches. 
     In some embodiments, the ultrasound device is configured to control the frequency of the clock signal, at least in part, by switching on a certain number of the plurality of current source unit cells with respective drain switches and a certain number of the plurality of current source unit cells with respective source switches. 
     In some embodiments, the ultrasound device may further comprise control circuitry comprising coarse control circuitry configured to control how many blocks of one or more of the plurality of current source unit cells with respective drain switches and/or one or more of the plurality of current source unit cells with respective source switches are turned on. 
     In some embodiments, each of the plurality of current source unit cells with respective drain switches and each of the plurality of current source unit cells with respective source switches is coupled to an output terminal of a resistor-capacitor (RC) filter, a ratio between a decrease in voltage at the output terminal of the RC filter caused by one of the plurality of current source unit cell with respective drain switches switching on to an increase in voltage at the output terminal of the RC filter caused by one of the current source unit cell with respective source switches switching on is m:n, each or approximately each of the blocks comprises 1+floor (n/m) current source unit cells with a composition of floor (n/m) current source unit cells with respective drain switches and one current source unit cell with respective source switches. 
     According to an aspect of the present application, a method is provided, the method comprising using an ultrasound device comprising a phase-locked loop (PLL) comprising a digitally-controlled oscillator (DCO) comprising a plurality of current source unit cells with respective drain switches. and a plurality of current source unit cells with respective source switches, wherein using the ultrasound device comprises switching on a certain number of the plurality of current source unit cells with respective drain switches and a certain number of the plurality of current source unit cells with respective source switches. 
     In some embodiments, the plurality of current source unit cells with respective drain switches have a first circuit topology, the plurality of current source unit cells with respective source switches have a second circuit topology, and the first and second circuit topologies are different. 
     In some embodiments, the PLL is configured to use a fast switching technique that allows the PLL to power down when the ultrasound device is not generating data and to power up within 1 microsecond when the ultrasound device begins to generate data again. 
     In some embodiments, switching on one of the plurality of current source unit cells with respective drain switches causes a voltage transition at an internal node of the current source unit cell with respective drain switches proceeding in a first voltage direction, switching on of the plurality of current source unit cells with respective source switches causes a voltage transition at an internal node of the current source unit cell with respective source switches proceeding in a second voltage direction, and the first and second voltage directions are different. 
     In some embodiments, each of the plurality of current source unit cells with respective drain switches comprises a switch, and a current source wherein the current source comprises a first terminal and a second terminal and the switch is coupled to the first terminal of the current source and each of the plurality of current source unit cells with respective source switches comprises the switch, and the current source wherein the switch is coupled to the second terminal of the current source. 
     In some embodiments, the current source comprises a single transistor, the first terminal comprises a drain of the transistor, and the second terminal comprises a source of the transistor. 
     In some embodiments, the current source comprises a cascode current source that comprises multiple transistors, the first terminal comprises a drain of one of the multiple transistors, and the second terminal comprises a source of the one of the multiple transistors. 
     In some embodiments, the switch comprises a single transistor. 
     In some embodiments, the switch comprises a transmission gate. 
     In some embodiments, the current source comprises at least one transistor having a gate terminal, and the gate terminal is coupled to an output of a resistor-capacitor (RC) filter. 
     In some embodiments, the RC filter is coupled to an output terminal of bias generation circuitry. 
     In some embodiments, the switch comprises at least one transistor having a gate terminal, the PLL comprises a decoder having a plurality of output terminals and the gate terminal of the transistor is coupled to one of the plurality of output terminals of the decoder. 
     In some embodiments, the DCO comprises a ring oscillator, and each of the plurality of current source unit cells with respective drain switches and each of the plurality of current source unit cells with respective source switches is couplable to the ring oscillator. 
     In some embodiments, using the ultrasound device comprises using the ring oscillator is configured to generate a clock signal having a frequency that depends on an amount of current that the ring oscillator receives from the plurality of current source unit cells with respective drain switches and the plurality of current source unit cells with respective source switches. 
     In some embodiments, using the ultrasound device comprises controlling the frequency of the clock signal, at least in part, by switching on the certain number of the plurality of current source unit cells with respective drain switches and the certain number of the plurality of current source unit cells with respective source switches. 
     In some embodiments, the ultrasound device further comprises control circuitry comprising coarse control circuitry and using the ultrasound device comprises using the coarse control circuitry to switch on or off of blocks comprising one or more of the plurality of current source unit cells with respective drain switches and or more of the plurality of current source unit cells with respective source switches at a time. 
     In some embodiments, each of the plurality of current source unit cells with respective drain switches and each of the plurality of current source unit cells with respective source switches is coupled to an output terminal of a resistor-capacitor (RC) filter, the RC filter is coupled to an output terminal of bias generation circuitry, a ratio between a decrease in voltage at the output terminal of the RC filter caused by one of the plurality of current source unit cell with respective drain switches switching on to an increase in voltage at the output terminal of the RC filter caused by one of the current source unit cell with respective source switches on is m:n, each or approximately each of the blocks comprises 1+floor (n/m) current source unit cells with a composition of floor (n/m) current source unit cells with respective drain switches and one current source unit cell with respective source switches. 
     According to an aspect of the present application, an ultrasound device is provided, the device comprising a plurality of ultrasound transducers, serializer-deserializer (SerDes) circuitry coupled to the plurality of ultrasound transducers, and a phase-locked loop (PLL) comprising a plurality of current source unit cells of a first type and a plurality of current source unit cells of a second type different from the first type. 
     In some embodiments, the at least one of the plurality of current source unit cells of the first type is configured to produce a first voltage increase when turned on, and wherein at least one of the plurality of current source unit cells of the second type is configured to produce a first voltage decrease when turned on. 
     In some embodiments, the at least one of the plurality of current source unit cells of the first type is configured to produce a second voltage decrease when turned off, and wherein the at least one of the plurality of current source unit cells of the second type is configured to produce a second voltage increase when turned off. 
     In some embodiments, the least one of the plurality of current source unit cells of the first type comprises a drain switch and at least one of the plurality of current source unit cells of the second type comprises a source switch. 
     In some embodiments, the source switch comprises a transmission gate. 
     In some embodiments, the source switch comprises a cascode current source. 
     According to an aspect of the present application, a method is provided for operating an ultrasound device, the method comprising producing a plurality of electric signals using a plurality of ultrasound transducers, combining the plurality of electric signals using serializer-deserializer (SerDes) circuitry, wherein the combining comprises timing the SerDes circuitry using a phase-locked loop (PLL) at least in part by turning on a plurality of current source unit cells of a first type and at least in part by turning on a plurality of current source unit cells of a second type different from the first type. 
     In some embodiments, turning on the plurality of current source unit cells of the first type and turning on the plurality of current source unit cells of the second type comprises determining how many current source unit cells of the first type and how many current source unit cells of the second type should be turned on to limit a voltage disturbance. 
     In some embodiments, determining how many current source unit cells of the first type and how many current source unit cells of the second type should be turned on to limit the voltage disturbance comprises identifying a plurality of entries of a look-up table, that, collectively, yield a voltage disturbance below a predefined threshold. 
     While the above description has described various circuitry and methods for operating such circuitry in the context of ultrasound devices, the circuitry and methods may be used in the context of other electronic devices as well. 
     The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.” 
     The phrase “and/or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with “and/or” should be construed in the same fashion, i.e., “one or more” of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the “and/or” clause, whether related or unrelated to those elements specifically identified. 
     As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified. 
     Use of ordinal terms such as “first,” “second,” “third,” etc., in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements. 
     As used herein, reference to a numerical value being between two endpoints should be understood to encompass the situation in which the numerical value can assume either of the endpoints. For example, stating that a characteristic has a value between A and B, or between approximately A and B, should be understood to mean that the indicated range is inclusive of the endpoints A and B unless otherwise noted. 
     The terms “approximately” and “about” may be used to mean within ±20% of a target value in some embodiments, within ±10% of a target value in some embodiments, within ±5% of a target value in some embodiments, and yet within ±2% of a target value in some embodiments. The terms “approximately” and “about” may include the target value. 
     Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having,” “containing,” “involving,” and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. 
     Having described above several aspects of at least one embodiment, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be object of this disclosure. Accordingly, the foregoing description and drawings are by way of example only.