Patent Publication Number: US-9853560-B2

Title: Congruent power and timing signals for device

Description:
BACKGROUND 
     Systems and devices often rely upon two kinds of signals for operation. A power signal may be used to provide power, logic, and control signals within a system or device. Further, a timing signal or clock signal may also be used to trigger, manipulate or otherwise control various components and circuits of a system or device. Thus, together, these two kinds of signals may be used accordingly. 
     Often times, a system or device may have the above-described signals provided externally from the system or device. That is, the power signal and/or the clock signal may originate from a circuit outside the system or device. For example, when monitoring overhead power lines, a device for monitoring may draw power directly from the power lines themselves. Similarly, in a device having multiple integrated circuit (IC) chips or multiple separate printed circuit boards (PCB), a single clock source may provide timing signals for all components in a device. Furthermore, these signals, when originating outside of ICs, PCBs, or specific separate devices, may require isolation before being used within these components. As such, both the power signals and the timing signals may require isolating transformers for each kind of signal to provide the isolated signals for use on-chip. Providing two isolating transformers for these two sets of signals is cumbersome and inefficient. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the subject matter disclosed herein will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings. 
         FIG. 1  is a block diagram of a conventional system for providing a power signal and a timing signal to a device using two different isolation transformers. 
         FIG. 2  is a block diagram of a system for providing a power signal and a timing signal to a device using one isolation transformer according to an embodiment of the subject matter disclosed herein. 
         FIG. 3  is a block diagram of a system for providing a power signal and a timing signal to devices of a three-phase power system using one isolation transformer per device according to an embodiment of the subject matter disclosed herein. 
     
    
    
     DETAILED DESCRIPTION 
     The following discussion is presented to enable a person skilled in the art to make and use the subject matter disclosed herein. The general principles described herein may be applied to embodiments and applications other than those detailed above without departing from the spirit and scope of the present detailed description. The present disclosure is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed or suggested herein. 
     Prior to discussing the specific details of various embodiments, an overview of one embodiment of the subject matter is presented. Electronic circuits may often use two different kinds of signals as discussed above—power signals and clock signals. According to various embodiment discussed below, a single signal may be used to provide both a power signal and a clock signal to a circuit via a single isolation transformer. In one embodiment, an integrated circuit may include just one isolation transformer operable to generate an isolated signal on its secondary side that is proportional to an initial signal received from a signal source. On the secondary side, two branches may then extract both a power signal and a clock signal for use in the circuit on the isolated secondary side. The first branch may be coupled to the transformer and operable to manipulate the signal into a power signal, such as a 5V DC signal. Likewise, the second circuit branch is operable to manipulate the signal into a clock signal, such as a 5 V signal with a frequency of 1 MHz. By extracting both a power supply signal and a clock signal from the same isolation transformer on the secondary side, valuable space may be saved on an integrated circuit device with only having a single winding for a single isolation transformer. These and other aspects of the embodiments are discussed below in greater detail. 
       FIG. 1  is a block diagram of a conventional system for providing a power signal and a timing signal to a device using two different isolation transformers. In this system  100 , a clock source  110  (which may be external to the IC, PCB, or device  105 ) may provide an initial clock signal to the primary side of a first isolation transformer  111 . The isolation transformer then translates the signal into a secondary-side signal that be used to provide a clock signal CLK to an IC  105  (hereinafter, reference to an IC  105  is understood to mean an IC, PCB, or other component/device). The secondary side of the first isolation transformer  111  is also coupled to a ground GND. 
     Similarly, yet separately, a power source  120  (again, possibly external) may provide a power signal to the primary side of a second isolation transformer  121 . The second isolation transformer then translates a power signal on its secondary side to provide such the power signal Vcc to the IC  105 . As before, the secondary side of the second isolation transformer  121  may also be coupled to the ground GND. 
     In this manner, both a power signal Vcc and a clock signal CLK are generated external to the IC  105 , yet provided to the IC in an isolated manner through the two different isolation transformers  110  and  120 . However, with two different isolation transformers  110  and  120 , more space is required for the two different transformer windings. Space may be at a premium in smaller and more efficient devices and the requirement for two different sets of transformer windings is a disadvantage. As is described with respect to  FIG. 2 , however, if the clock signal can be “piggy-backed” onto the power signal, then only a single isolation transformer may be needed. 
       FIG. 2  is a block diagram of a circuit  200  for providing a power signal and a timing signal to a device using one isolation transformer according to an embodiment of the subject matter disclosed herein. In this embodiment a power/clock source  225  may provide a signal having a specific frequency and amplitude. A suitable frequency may be 1 MHz and a suitable voltage magnitude may be 12 V. Since common power sources may be different (e.g., a North American Standard of 120 V and 60 Hz), such a 12 V, 1 MHz signal may be derived according to conventional solutions for changing the frequency and voltage amplitude of a signal. In this example and the following example below with respect to  FIG. 3 , the original signal may be a common power line source having an initial frequency of 60 Hz and 240 V. Such conventional manners of manipulating a voltage signal are not discussed in greater detail herein. 
     The power/clock source  225  provides a signal to the primary side of a single isolation transformer  230 . The isolation transformer  230  then generates an almost identical signal at its secondary winding since the isolation transformer has an equivalent number of windings on each side. The initial 12V, 1 MHz signal passes through a filter capacitor  250  to filter out any low-end transients. After this initial filtering, the oscillating (and now filtered) signal may be manipulated in one two ways to deliver either a clock signal to the component  205  or a power signal to the component  205 . 
     In the case of the power signal manipulation, the circuit includes zener diode  253  connected between the output of the filter capacitor and ground GND. The zener diode  253  is sized so as to clamp the magnitude of the voltage of the signal at node  260  to 5 V. The circuit then further includes a rectifying diode  252  that rectifies the clamped signal to provide a DC supply voltage to the Vcc node of the component  205 . This DC supply voltage is filtered a second time by filter capacitor  254  to remove any high-frequency transients. Thus, a filtered, rectified, and clamped 5V power signal is delivered to Vcc. 
     In the case of the clock signal manipulation, the zener diode  253 , as described above, clamps the signal at node  260  to 5 V. Node  260  is coupled to the clock input CLK of the component  205  through an impedance  251 . This impedance  251  may be sized to further reduce the voltage of the clock signal as it enters the clock node. Further, without any rectification, the frequency of the clock signal will be the same as the frequency of the initial power/clock signal from the secondary winding of the isolation transformer  230 . 
     Such a solution is advantageous because both the clock signal CLK and the power signal Vcc may be derived from a single signal that passes through a single isolation transformer  230 . Having only a single isolation transformer  230  reduces the space needed in a device or on an IC or PCB because of the reduced number of windings in the single transformer. When IC space is at a premium, such a reduction in winding space provides a distinct advantage. Thus, the circuit  200  may be part of a larger system as discussed below with respect to  FIG. 3 . 
       FIG. 3  is a block diagram of a system  300  for providing a power signal and a clock signal to measurement devices of a three-phase power system using one isolation transformer per device according to an embodiment of the subject matter disclosed herein. Such a system  300  may be used within the context of a three-phase power distribution system. For example, the system  300  may include a set of power lines having four conductors, phase A  310   a , phase B  310   b , phase C  310   c  and a neutral conductor  311 . Often times, it may be useful to know the voltage and current characteristics at any point in time for each of these conductors. Thus, each conductor may be coupled to both a dedicated current sensor  320   a - c  and a dedicated voltage sensor  321   a - c.    
     In the system of  FIG. 3  then, phase A  310   a  may be coupled to a first voltage sensor  321   a  and a first current sensor  320   a . Similarly, phase B  310   b  may be coupled to a second voltage sensor  321   b  and a second current sensor  320   b  just as phase C  310   c  may be coupled to a third voltage sensor  321   c  and a third current sensor  320   c . A skilled artisan understands that each of these sensors may include circuitry for generating signals proportional to the voltages and currents on the conductors as handling such large voltages and currents directly may be dangerous. As such, these values are transformed to signals better suited for use in the circuits  302   a - c.    
     In this system  300  embodiment, several devices and/or components may be powered from a single source that may or may not be part of the same circuit and/or IC in the system. Here, there are four different circuits shown in the system  300  of  FIG. 3 . A first circuit  340  may be used to provide a common power/clock signal to each of the other three circuits  302   a - c . Each of these three circuits  302   a - c  may comprise the circuit  200  shown in  FIG. 2 . In this manner, each circuit  302   a - c  may be provided a single power/clock signal such that each circuit only includes one isolation transformer. Further, each of these circuits  302   a - c  may be coupled to respective currents sensors  320   a - c  and respective voltage sensors  321   a - c  to receive measurement signals from the actual conductors  310   a - c  of the three-phase power system. 
     The first circuit  340  may be coupled to a voltage source for initially generating a power signal. In one embodiment, this power source may be one of the power lines; as shown, the circuit  340  is coupled to the voltage sensor  321   c  for Phase C  310   c . In other embodiments, this initial power source may be a battery or other suitable power source. The circuit  340  may then manipulate the initial power signal to provide a suitable power/clock signal to the other three circuits  302   a - c . Further, the first circuit may include a processor  390  operable to perform calculations based upon data received back from other circuits in the system. Further yet, calculated data may be stored in a memory  391 . 
     Thus, the power/clock signal is initially provided as a clock signal with a frequency of 1 MHz which will have a relatively low magnitude. This signal is conditioned by impedance  331 . So, instead providing this clock signal directly to the three circuits  302   a - c , the clock signal is used to drive a switching transistor  330  that switches a 12-volt supply voltage through the primary side of each isolation transformer for each respective circuit  302   a - c . Further, a filter capacitor  332  filters out low-frequency transients. In this manner, each circuit is provided with a power/clock signal having a voltage of 12 V and a frequency of 1 MHz. 
     Such a circuit  340  for generating the power/clock signal may be other configurations. Any circuit that can generate an oscillating signal with a specific voltage magnitude and frequency may be used to generate the power/clock signal. Furthermore, any type of filtering arrangement on the secondary side of each isolation transformer may be used to drive the IC supply voltages. Further yet, any type of separate filtering could be used to recover the clock signal for use at the IC as well. 
     On particular alternative technique generating a power/clock signal may be a circuit having a feedback signal from the secondary side of each circuit  302   a - c . Such a feedback signal would be sent back through the respective isolation transformer, but could then be used to modulate the duty cycle of the initial clock signal. By maintaining the frequency of the initial clock signal (e.g., leading edges of pulses still occur at a 1 MHz frequency), one could modulate the duty cycle to modulate the power delivered (e.g., the length of each pulse could vary). 
     Within the context of the system of  FIG. 3 , one could use the three circuits  302   a - c  for measuring the current and voltage characteristics of each phase  310   a - c . Each of these circuits  302   a - c  may include an IC (such as  205  from  FIG. 2 ) that may be include Sigma Delta modulators that may be used to sense current and voltage on a particular phase of a power supply. So for example, in the case of a three-phase power supply, one could use information garnered from these circuits  302   a - c  to calculate the entire power usage based on the readings from each phase. Additional information could be garnered from the neutral conductor  311  as well if one were couple a sensor (not shown) here as well. 
     Each of the circuits  340  and  302   a - c  as well as the sensors  320   a - c  and  321   a - c  may be housed within a single device such as a power meter. Alternatively, the sensors  320   a - c  and  321   a - c  may be housed in separate dedicated devices that may be located near the conductors  310   a - c , such that only small measurement signals are sent to a separate device housing the additional circuits of the system  300 . Further yet, all circuits described in the system of  FIG. 3  may be resident on a single IC. 
     While the subject matter discussed herein is susceptible to various modifications and alternative constructions, certain illustrated embodiments thereof are shown in the drawings and have been described above in detail. It should be understood, however, that there is no intention to limit the claims to the specific forms disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the claims.