Patent Publication Number: US-7588539-B2

Title: Integrated low-power pw/cw transmitter

Description:
REFERENCE TO RELATED APPLICATIONS 
   The present patent document claims the benefit of the filing date pursuant to 35 U.S.C. §119(e) of Provisional U.S. Patent Application Ser. No. 60/538,449, filed Jan. 21, 2004, which is hereby incorporated by reference. 

   BACKGROUND 
   The present invention relates to ultrasound transmitters. In particular, a transmitter is operable for both pulsed wave and continuous wave modes. 
   Ultrasound transmitters include waveform generators for generating different types of waveforms. Pulsed waveforms are relatively high voltage waveforms, such as 20-200 volt peak amplitude, of short duration, such as one to three cycles. Unipolar or bipolar pulsed waves may be generated using one or more transistors. The transistors are switched on and off, connecting a high voltage sources (±) or ground to an output. For continuous wave operation, a multi-cycle waveform, such as ten or more cycles (e.g., generating MHz waveforms for minutes), with relatively lower voltage, such as 2.5 to 12 volts, is generated. Transistors for operating at high voltages inefficiently operate at lower voltages. 
   Many ultrasound systems use separate circuits for generating pulsed and continuous waves. Separate circuits are provided in different application specific integrated circuits, chips or even boards. The low voltage circuitry for continuous wave operation is not subjected to the high voltages of the pulsed waves. 
   Where space, power availability or heat dissipation restrictions exist, sacrifices in the types of waves transmitted may result. For example, transmitters integrated into a multi-dimensional transducer array housing have been developed to provide pulsed waveform generation. However, efficient continuous wave operation is still desired even for real-time three-dimensional imaging provided by multi-dimensional arrays with integrated transmitters. 
   BRIEF SUMMARY 
   By way of introduction, the preferred embodiments described below include methods and systems for ultrasound imaging with both pulsed and continuous waves. High voltage and low voltage switches are integrated onto a same semiconductor chip. The high voltage switches are used for pulsed wave operation, and the low voltage switches are used for continuous wave operation. Power dissipation may be reduced by using low voltage circuits for the continuous wave operation. Both the pulsed and continuous waveforms are output on a common output from the integrated circuit. For continuous wave operation, one or more of the high voltage switches is used to provide a low resistance path to the common output or ground. For pulsed wave operation, one or more of the low voltage switches is used to provide a low resistance path to a common output or ground. A switch used for generating waveforms is also used for forming a low resistance path. 
   In a first aspect, a transmitter is provided for ultrasound imaging with pulsed and continuous wave operation. The transmitter is improved by having high and low voltage switches integrated on a same circuit and having a common waveform output for the circuit. 
   In a second aspect, a waveform generator is provided for ultrasound imaging. At least a first higher voltage switch is integrated on a chip. At least a first lower voltage switch is also integrated on the chip with the first higher voltage switch. An output is provided on the chip. The output is connected with the first higher voltage switch and the first lower voltage switch. 
   In a third aspect, a method is provided for generating a transmit waveform as either of pulsed and continuous waves. Pulse waves are generated with high voltage switches in an integrated circuit. Continuous waves are generated with low voltage switches in the integrated circuit. A low or zero voltage is connected to at least one of the high voltage switches with at least one of the low voltage switches during generation of pulsed waves. The pulsed waves, when generated, and the continuous waves, when generated, are output on a common output from the integrated circuit. 
   The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims. Further aspects and advantages of the invention are discussed below in conjunction with the preferred embodiments and may be later claimed independently or in combination. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The components and the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like reference numerals designate corresponding parts throughout the different views. 
       FIG. 1  is a circuit diagram of one embodiment of a integrated circuit for ultrasound imaging; 
       FIG. 2  is a cross-sectional diagram of one embodiment of a transducer incorporating the integrated circuit of  FIG. 1 ; 
       FIG. 3  is a table of one embodiment of the switch states for operation of the waveform generator of  FIG. 1 ; and 
       FIG. 4  is a flowchart diagram of one embodiment of a method for generating a transmit waveform as either of pulsed and continuous waves. 
   

   DETAILED DESCRIPTION OF THE DRAWINGS AND PRESENTLY PREFERRED EMBODIMENTS 
   While high voltage switches used for pulsed wave generation may be used to also generate continuous waves, such use is inefficient and results in high power dissipation. Where power dissipation is a concern, such as in transmitters integrated within a transducer handle, high voltage switches may be undesirable for low voltage continuous wave operation. By integrating a low voltage pulser with a high voltage pulser, both pulsed and continuous wave operation is provided with more limited power dissipation. The high voltage and low voltage switches, such as field effect transistors, are integrated within a same application specific integrated circuit. The common waveform output for both the pulsed and continuous wave pulses provides further integration. During pulse wave operation, low voltage switches are maintained in a steady state. For continuous wave operation, the high voltage switches are maintained in a steady state. One high voltage switch is used for routing the continuous wave to the common output during continuous wave operation. The low voltage pulser is protected from high voltage exposure. During pulsed wave operation, one of the low voltage switches is used for forming a low resistance path to a ground or other steady state voltage. 
     FIG. 1  shows one embodiment of a transmitter with a waveform generator for ultrasound imaging. The transmitter generates waveforms for both pulsed and continuous wave operation. The waveform generator and transmitter are integrated in a same circuit or chip  10 . For example, an application specific integrated circuit  10  having one or more of the transmitters shown in  FIG. 1  is provided. The different components and waveform generators are formed using the same or different processes on the same semiconductor substrate, such as using CMOS processes. 
   The integrated circuit  10  includes high voltage switches  12 ,  14 , low voltage switches  16 ,  18 , controller (high voltage gate driver)  20 , controller (low voltage gate driver)  22 , a common output  24 , a ground, return line or other low impedance point connector  26 , a high voltage power supply connector  28 , a low voltage power supply connector  30 , a mode input  32 , a pulse timing input  34 , and an enable input  36 . Additional, different or fewer components may be provided. For example, additional high voltage or low voltage switches are provided. As another example, the controllers  20 ,  22  are formed as a single controller. As another example, an oscillator is included within the integrated circuit  10  for providing the timing information without a separate timing input  34 . As yet another example, a single voltage connector is provided and divided or otherwise reduced to provide different voltages within the integrated circuit  10 . As yet another example, additional inputs are provided for operating the controllers  20 ,  22  and/or the switches  12 - 18 . 
   The integrated circuit  10  is operable to generate either pulsed or continuous waves. The common output  24  connects directly or indirectly with a transducer element for converting the generated waveform into acoustic energy. In the embodiment shown in  FIG. 1 , the continuous or pulsed waveforms are unipolar waveforms, but bipolar or more complex waveforms may be generated for either or both of continuous or pulsed wave operation. 
   The high voltage switches  12 ,  14  form a waveform generator and are complimentary field effect transistors, but may include other types of transistors or switches. Each of the high voltage switches  12 ,  14  may be of a same or different type of switch. Each high voltage switch  12 ,  14  has a turn-on threshold greater than 6 volts, such as being a 7 to 8 volt threshold. Greater or lesser threshold voltages may be provided. The high voltage switches  12 ,  14  are operable with at least 10 or more volts, such as allowing for a 10 to 200 volt supply at the input  28 . A lower voltage may be provided, such as a voltage lower than the highest voltage for operating with continuous waves. For example, each of the high voltage switches  12 ,  14  is sized to have a gate oxide and other associated dimensions for operating with the 200 volt power supply. The drain-to-source resistance in the “on” state may be of any of various values, such as being 500 or less ohms. The high voltage switches  12 ,  14  are integrated on a same chip or within a same circuit. 
   The low voltage switches  16 ,  18  form a waveform generator and are complimentary field effect transistors, but other switches or transistors may be used. The low voltage switches  16 ,  18  may be of a same type or different type of switches from each other. Each low voltage switch  16 ,  18  has a turn-on threshold of less than 6 volts, such as a 1 to 2 volt threshold. Greater or lesser threshold voltages may be provided. The low voltage switches  16 ,  18  have a thinner oxide layer at the gate or other differences in dimensions for operation with exposure to a lesser voltage than the high voltage switches  12 ,  14 . In one embodiment, the low voltage switches  16 ,  18  are smaller than the high voltage switches  12 ,  14 . For example, the low voltage switches  16 ,  18  are operable with voltage supplies less than 10 volts, such as voltages input on the low voltage input  30  of 2.5 to 12 volts. The switching rate for the low voltage switches  16 ,  18  may be slower, the same or faster than the switching rate of the high voltage switches  12 ,  14 . The drain-to-source resistance of the low voltage switches  16 ,  18 , and the low voltage switch in  18  in particular, is much lower, such as ten times smaller than the drain to source resistance of the high voltage switch  14 . For example, the resistance of the low voltage switches  16 ,  18  is 50 ohms or less. Lesser resistance is provided by having a smaller size. Greater resistances may be provided with a similar or different ratio of resistances from the high voltage switches  12 ,  14  to the low voltage switches  16 ,  18 . 
   The low voltage switches  16 ,  18  are integrated on the same chip and associated circuit  10  as the high voltage switches  12 ,  14 . The same semiconductor substrate is used for both the high voltage and low voltage switches  12 - 18 . 
   The high voltage switch  12  connects between (a) the high voltage input  28  and (b) the common output  24  and other high voltage switch  14 . During pulse wave operation, the high voltage switch  12  alternately connects and disconnects the common output  24  to the high voltage input  28 . During continuous wave operation, the high voltage switch  12  is open to prevent high voltage at the input  28  from connection with the low voltage switches  16 ,  18  or common output  24 . 
   The high voltage switch  14  connects between (a) the high voltage switch  12  and the common output  24  and (b) the low voltage switches  16 ,  18 . During pulsed wave operation, the high voltage switch  14  alternately connects and disconnects the low voltage switches  16 ,  18  to the common output  24 . The high voltage switch alternates opposite to the other high voltage switch  12 . During continuous wave operation, the high voltage switch  14  is closed, providing a low resistance path from the low voltage switches  16 ,  18  to the common output  24 . 
   The high voltage switches  12 ,  14  form a simple switching pulser. More complex pulsers may be provided using a greater number of switches.  FIG. 1  shows a pulsed waveform as a single pulse generated by the high voltage switches  12 ,  14 . A threshold voltage of 5 to 10 volts is used to turn on and off the high voltage switches  12 ,  14  for generating a pulsed waveform with a 10 to 200 volt peak amplitude. If the high voltage provided on a high voltage input  28  is reduced, such as for continuous wave operation, to a level used to drive the high voltage switches  12 ,  14 , such as 12 volts shown by V dx , the peak-to-peak voltage at the gates of the high voltage switches  12 ,  14  becomes comparable to the output voltage swing on the common output  24 . This results in inefficient operation. By providing the low voltage switches  16 ,  18  operable in response to a lower gate or threshold voltage, more efficient continuous wave operation is provided. 
   The low voltage switch  16  connects between (a) the low voltage input  30  and (b) the high voltage switch  14  and the low voltage switch  18 . During continuous wave operation, the low voltage switch  16  alternately connects and disconnects the low voltage on the low voltage input  30  to the common output  24  through the closed high voltage switch  14 . During pulsed wave operation, the low voltage switch  16  is open. The low voltage input  30  is disconnected from the path from the high voltage switch  14  through the low voltage switch  18  to the ground or other voltage on the connection  26 . 
   The low voltage switch  18  is connected between (a) the low voltage switch  16  and the high voltage switch  14  and (b) the connector  26 . The connector  26  provides a ground or other output or input connection, such as a diode clipped substantially constant low voltage. For continuous wave operation, the low voltage switch  18  alternately connects and disconnects the connector  26  with the common output  24  through the high voltage switch  14 . The low voltage switch  14  connects the ground or other limited voltage to the common output  24 . The low voltage switch  18  alternates states opposite of the other low voltage switch  16 . By alternating states, a continuous waveform extending from the ground or other voltage at the connector  26  with a peak voltage provided by the low voltage input  30  is generated as shown in  FIG. 1 . More complex pulsers with a greater number of switches may alternatively be provided. During pulsed wave operation, the low voltage switch  18  is closed, providing a low resistance path from the high voltage switch  14  to ground or other voltage provided at the connector  26 . 
   Since the low voltage switches  16 ,  18  are integrated on the same semiconductor, an improved performance in power dissipation for continuous wave operation is provided. The lower threshold voltages of the low voltage switches  16 ,  18  require less peak-to-peak gate voltage to turn the switches  16 ,  18  on and off. As a result, less energy is required for each gate transition. Since the threshold voltage of the smaller low voltage switches  16 ,  18  is similar to or less than the peak voltage for the continuous wave forms, the low voltage pulser operates in an efficient manner. The high voltage circuitry, including the controller  20  and the high voltage switches  12 ,  14 , are static during continuous wave operation, so do not contribute significantly to power dissipation except for parasitic capacitive loading effects. 
   The continuous and pulsed waveforms generated by the high voltage or low voltage switches  12 - 18  are output on the common output  24 . The common output  24  is a signal trace, a connector, conductor or other device for electronically connecting the integrated circuit  10  on the semiconductor chip with external components. The common output  24  is connected with the two high voltage switches  12 ,  14  for receiving a pulsed wave. The common output  24  connects with the two low voltage switches  16 ,  18  through one of the high voltage switches  14  for receiving a continuous wave. In alternative embodiments, the common output  24  directly connects to one of the low voltage switches  16 ,  18 , such as connecting to the high voltage and low voltage switches in parallel or connecting to the high voltage switches  12 ,  14  through one or more of the low voltage switches  16 ,  18 . The common output  24  allows connection to a given ultrasound transducer element or other component without additional switching to select between the high voltage and low voltage pulsers integrated on the same circuit  10  or semiconductor chip. 
   The connector  26  is an input connection to ground in one embodiment. In other embodiments, a constant DC voltage other than zero volts is input. In yet other alternative embodiments, the connector  26  connects with receiver circuitry. Diodes are used to clip the positive and negative going voltages to a substantially low value, effectively grounding the connector  26  for operation of the high voltage and low voltage pulsers. 
   The high and low voltage controllers  20 ,  22  includes transistors, gate drivers or other devices for receiving inputs and controlling the high voltage switches  12 ,  14  and low voltage switches  16 ,  18  in response to inputs. For example, an enable signal is provided on the enable input  36  for allowing the operation of the controllers  20 ,  22 . A mode signal input on the mode input  32  indicates whether the high voltage switches  12 ,  14  are to be operated for a pulsed wave mode or the low voltage switches  16 ,  18  in a continuous wave mode. After enabling the controllers  20 ,  22  and configuring the controllers  20 ,  22  for operation pursuant to the desired mode, one or both of the controllers  20 ,  22  is responsive to the pulse signal on timing input  34  for generating a single one or a sequence of pulses.  FIG. 3  shows a table of states of the high voltage switches  12 ,  14  and low voltage switches  16 ,  18  in response to the enable, mode and pulsing input signals. During continuous wave operation, the high voltage controller  20  maintains the state of the high voltage switches  12 ,  14 , and the low voltage controller  22  causes the low voltage switches  16 ,  18  to alternate states. During pulse wave operation, the low voltage controller  22  causes the low voltage switches  16 ,  18  to maintain a state, and the high voltage controller  20  causes the high voltage switches  12 ,  14  to alternate states. Additional, different or fewer controls may be provided. For example, the powered down mode may be associated with all of the switches  12 - 18  in an off state. The controls are all low voltage CMOS inputs, such as 5 volt inputs, but other voltage levels or multiple voltage levels may be used. 
   The voltage provided at the low voltage input  30  and the high voltage input  28  is supplied by fixed or variable voltage sources. Other voltage regulators may be provided, such as providing for a voltage supply or regulation integrated within the integrated circuit  10 . 
   The integrated circuit  10  is used within an ultrasound system. For example, a coaxial cable connects the common output  24  to a transducer element of an ultrasound array. In another embodiment shown in  FIG. 2 , the integrated circuit  10  is positioned within a transducer housing  50  for connection to a multi-dimensional array  52 . The common output  24  connects with one or more elements of the array  52 . By integrating both high and low voltage switches in the same integrated circuit  10 , continuous and pulsed wave operation may be provided with lesser power dissipation. By operating only low voltage switches  16 ,  18  for continuous wave operation, less power is consumed. Less power consumption results in a lesser generation of heat. Similarly less power dissipation may be desired for use with battery operated or other restricted power supplies. The relationship between continuous wave and pulsed wave power dissipation of a single pulser is roughly defined by P pw /P cw =(V pp   2 DF pw )/(V cw   2 ) where DF pw  is the duty factor for the pulse waveform mode, V pp  is the high power voltage and V cw  is the low power voltage. The duty factor for the pulse wave mode ranges between 0.1% and 1%. For a high voltage of 200 volts and a low voltage of 12 volts, the ratio of the pulsed waveform to the continuous waveform powers is between 0.28 and 2.8. The continuous wave power dissipation is reduced to the range of the pulsed wave power dissipation. Since continuous wave operation is associated with some elements operating on transmit and others operating on receive at a same time, a continuous wave aperture may be less than a pulse wave aperture. As a result, the reduction in size of the continuous wave transmit aperture also provides a reduction in power dissipation. 
   As compared to operation with just the pulsed wave components, the integrated circuit  10  provides for continuous wave operation with an input for the mode  32  and the low voltage input  30 . Both the mode and the low voltage inputs  30 ,  32  are common to a plurality of pulsers for use with the array  52  of elements. Additional per channel interconnections are accordingly limited. As a result, the board space and trace routing requirements for a plurality of application specific integrated circuits each implementing a plurality of transmitters and associated waveform generators is simplified. Since the high voltage switch  14  and low voltage switch  18  are used for protecting the low voltage switches  16  and  18  from the high voltage input  28  and for connecting the high voltage switch  14  to ground while sharing a common output, the circuit requirements may be reduced. For example, the common output  24  connects directly to the transducer elements without further integrated or external components for selecting between the two different types of pulsers. 
     FIG. 4  shows one embodiment of a method for generating transmit waveforms as either of pulsed and continuous waves from a same chip or integrated circuit. The method uses the integrated circuit  10  shown in  FIG. 1  or  FIG. 2 , but other integrated circuits, chips, transmitters, waveform generators or devices may be used. Additional, different or fewer acts than shown in  FIG. 4  may be provided. 
   In act  60 , connections are made for generating pulsed waves. A low, ground or substantially zero voltage is connected to a high voltage switch with a low voltage switch. A common output connects directly to one or more of the high voltage switches. Both the high voltage and low voltage switches are integrated within a same integrated circuit and semiconductor chip. In alternative embodiments, two or more high voltage switches are connected to the low, zero or ground voltage and/or two or more low voltage switches are used to provide the connection. 
   In act  62 , connections are performed for generating continuous waves. An output used for outputting both continuous and pulsed waves is connected to low voltage switches. One or more high voltage switches are used to perform the connection. Another high voltage switch isolates the low voltage switches from the high voltage source. 
   In act  64 , pulsed waves are generated with the high voltage switches in the integrated circuit. For example, the common output is switched between a high voltage source and a ground or substantially constant lower voltage. As another example, the common output is switched between a high positive voltage source and a high negative voltage source. During generation of the pulsed waveforms, one or more of the low voltage switches connects one or more of the high voltage switches to ground or other low voltage. 
   In act  66 , continuous waves are generated with low voltage switches in the integrated circuit. The common output is switched between the low voltage source and ground. As another example, the low voltage switches are switched between positive and negative low voltages. The resulting continuous wave is provided on an output common with or the same as used for pulse wave generation. During continuous wave operation, one or more of the high voltage switches connects the low voltage switches to the common output. 
   In act  68 , the pulse waves are output when generated, and the continuous waves are output when generated. Continuous and pulsed waves are generated at different times but share a common output from the same integrated circuit and associated semiconductor chip. The same transmitter and associated waveform generator may be used for generating either pulsed waves or continuous waves for different modes of ultrasound imaging. 
   While the invention has been described above by reference to various embodiments, it should be understood that many changes and modifications can be made without departing from the scope of the invention. It is therefore intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intended to define the spirit and scope of this invention.