Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J50/00—Circuit arrangements or systems for wireless supply or distribution of electric power
  • H02J50/80—Circuit arrangements or systems for wireless supply or distribution of electric power involving the exchange of data, concerning supply or distribution of electric power, between transmitting devices and receiving devices
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J50/00—Circuit arrangements or systems for wireless supply or distribution of electric power
  • H02J50/10—Circuit arrangements or systems for wireless supply or distribution of electric power using inductive coupling
  • H02J50/12—Circuit arrangements or systems for wireless supply or distribution of electric power using inductive coupling of the resonant type
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
  • H02J7/00032—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries characterised by data exchange
  • H02J7/00036—Charger exchanging data with battery
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
  • H02J7/00032—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries characterised by data exchange
  • H02J7/00045—Authentication, i.e. circuits for checking compatibility between one component, e.g. a battery or a battery charger, and another component, e.g. a power source
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B5/00—Near-field transmission systems, e.g. inductive or capacitive transmission systems
  • H04B5/20—Near-field transmission systems, e.g. inductive or capacitive transmission systems characterised by the transmission technique; characterised by the transmission medium
  • H04B5/24—Inductive coupling
  • H04B5/26—Inductive coupling using coils
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B5/00—Near-field transmission systems, e.g. inductive or capacitive transmission systems
  • H04B5/70—Near-field transmission systems, e.g. inductive or capacitive transmission systems specially adapted for specific purposes
  • H04B5/79—Near-field transmission systems, e.g. inductive or capacitive transmission systems specially adapted for specific purposes for data transfer in combination with power transfer

Definitions

• This relates to wireless power transfer between a power transmitter and a power receiver.
• Wireless power transfer is generally achieved by electromagnetic field coupling between a power transmitter and a power receiver.
• a primary electromagnetic field coupling component in the power transmitter generates an electromagnetic field that is picked up by a secondary electromagnetic field coupling component in the power receiver when the power receiver is placed near the power transmitter.
• the overall power receiving device (containing the power receiver) rectifies, conditions and/or regulates the received power as needed for the functioning of the device.
• Wireless Power Transfer Volume I: Low Power, Part 1 : Interface Definition, Version 1.0.2, April 2011) of the Wireless Power Consortium (the WPC standard) is an industry standard that sets forth a suitable description for implementing a wireless power transfer system (wireless power transmitter and wireless power receiver) and is incorporated herein by reference.
• the Qi Compliant Wireless Power Transmitter Manager bq500110 data sheet June 2010-Revised April 2011
• Qi Wireless Power Consortium
• Compliant bq51010, bq51011 and bq51013 data sheet September 2011-Revised May 2011
• Texas Instruments Incorporated are specific examples of a wireless power transmitter and wireless power receiver, respectively, and are incorporated herein by reference.
• the power transmitter In a typical wireless power transfer system design (including that of the WPC standard) the power transmitter generates an electromagnetic field through a primary inductor coil.
• a secondary inductor coil In a power pick-up unit with the overall power receiving device, a secondary inductor coil generates an AC current and voltage from the electromagnetic field.
• a rectification circuit rectifies the AC current and voltage to a DC current and voltage.
• a voltage regulator (or an output disconnect or a voltage conditioner, herein referred to as the voltage regulator) regulates the rectified voltage to a relatively constant or stable output voltage that can be used by the overall power receiving device to charge a battery or power its primary function circuitry.
• the secondary coil affects the electromagnetic field according to its resonant frequency and, thereby, changes the current through the primary inductor coil.
• This change in current can be used by the power transmitter to detect a load due to the presence of the power receiver and to receive communications from the power receiver. Controlling the amount of power wirelessly transferred from the power transmitter to the power receiver is thus achieved by sending feedback or error-signal communications from the power receiver to the power transmitter (e.g. to increase or decrease the transmitted power) by means of varying the resonant frequency of the secondary coil and, thus, the effect of the secondary coil on the electromagnetic field.
• the power receiver may periodically communicate its operating voltage, current and power levels or send commands for corrective actions required from the power transmitter to keep power receiver parameters within desired operating ranges.
• the power receiver typically communicates these signals, data or commands by modulating the load seen by the power transmitter with a differential bi-phase encoding scheme.
• the power receiver usually performs this modulation by switching on and off a modulation component (e.g. one or more capacitor, resistor or other dissipative component) that is typically placed before or after the rectification circuit in the power pick-up unit.
• the switching on and off of the modulation component generally changes the voltage level of the rectified voltage output by the rectification circuit and alters the resonant frequency in the secondary inductor coil. In this manner, the power receiver alters the coupling electromagnetic field between two states that the power transmitter can detect as logic bits in a data bit stream.
• a communication technique is illustrated by a set of graphs shown in Figs. 1, 2 and 3 as generated by a simulation of a typical prior art wireless power receiver as it communicates generic data or commands to a power transmitter.
• two sets of logic bits 100 and 101 (Fig. 1) are transmitted in a bit stream by the power receiver.
• the sets of logic bits 100 and 101 are encoded into a corresponding bit stream waveform 102 using a differential bi-phase encoding scheme.
• a fixed set of initial pulses 103 is added to the front of the logic bits 100 and 101 to form a modulation signal 104 that is used to modulate the load (i.e. switch on and off the modulation component) in the power receiver.
• the power transmitter thus, senses a series of changes in the coupling electromagnetic field that correspond to the modulation signal 104. When the power transmitter detects the initial pulses 103, it can proceed to properly decode the logic bits 100 or 101 that follow.
• Fig. 2 shows a simulated graph 105 of an example rectified voltage generated by the rectification circuit as the modulation component is switched on and off according to the modulation signal 104.
• communication time periods 106 when the logic bits 100 and 101 are being transmitted, typically a few tens of milliseconds, the rectified voltage changes between high and low levels representative of the modulation signal 104 with the encoded bit stream.
• pause time periods 107 when data is not being transmitted and the
• filtering capacitors on the rectification circuit output have to be relatively large due to the relatively large difference in average voltage over the relatively long duration of a cycle of the communication and pause time periods.
• the post-rectification voltage regulator has to operate at a relatively high headroom voltage due to the relatively large difference in average voltage.
• Embodiments of the invention generally involve a wireless power receiving device altering the electromagnetic field (e.g. between first and second states) in a manner that the wireless power transmitter can detect as a string of logic bits during communication time periods.
• the wireless power receiver also alters the electromagnetic field (e.g. between, or within a range between, the first and second states) during intervening pause time periods, but in a manner that the wireless power transmitter cannot detect as a string of logic bits.
• the rectified voltage in the power receiver is modulated during communication time periods at a frequency that allows the power transmitter to detect the resulting alterations in the electromagnetic field as communication logic bits.
• the rectified voltage is modulated at a different frequency that is too high for the power transmitter to detect the resulting alterations in the electromagnetic field as communication logic bits.
• the modulating at the higher frequency results in an average rectified voltage for the pause time periods being substantially similar to the average rectified voltage for the communication time periods, thereby allowing for maximizing the efficiency of the voltage regulator.
• a duty cycle of the higher frequency modulation is preferably selected to control the average rectified voltage level to better maximize the efficiency of the voltage regulator.
• Fig. 1 is a simplified set of prior art graphs for a bit stream waveform and a modulation signal for use in a prior art wireless power receiver.
• Fig. 2 is a simplified prior art graph of an example rectified voltage resulting from the modulation signal shown in Fig. 1.
• Fig. 3 is a simplified prior art graph of an average of the rectified voltage shown in Fig. 2.
• FIG. 4 is a simplified schematic diagram of a wireless power transfer system incorporating an embodiment of the invention.
• FIG. 5 is a simplified schematic diagram of a portion of a power pick-up unit in a wireless power receiving device incorporating an embodiment of the invention.
• FIG. 6 is an alternative simplified schematic diagram of a portion of a power pickup unit in a wireless power receiving device incorporating an embodiment of the invention.
• Fig. 7 is a simplified graph of a modulation signal for use in a wireless power receiving device according to an embodiment of the invention.
• Fig. 8 is a simplified graph of an example rectified voltage resulting from the modulation signal shown in Fig. 7 according to an embodiment of the invention.
• Fig. 9 is a simplified graph of an average of the rectified voltage shown in Fig. 8 according to an embodiment of the invention.
• Fig. 10 is the simplified graph of the average rectified voltage shown in Fig. 9, but at a finer y-axis resolution, according to an embodiment of the invention.
• Fig. 11 is a simplified graph of an alternative example rectified voltage resulting from the modulation signal shown in Fig. 7 according to an embodiment of the invention.
• Fig. 12 is a simplified graph of an average of the rectified voltage shown in Fig.
• the wireless power transfer system 109 generally includes a power transmitter 110 and a power receiving device 111.
• the power receiving device 111 may be any appropriate electronic device, such as a cell phone, game controller, electric toothbrush, clock, computer, microphone, etc. Electrical power is transferred from a primary inductor coil 112 in the power transmitter 110 to a secondary inductor coil 113 in the power receiving device 111 by means of electromagnetic field coupling.
• the power receiving device 111 modulates the electromagnetic field between first and second states in a manner that can be detected by the power transmitter 110 as logic bits in a communication bit stream.
• the power receiving device 111 continues to modulate the electromagnetic field between the same states (or within a range that is between the two states) during pause time periods between the communication time periods, but in a manner that cannot be detected by the power transmitter 110 as logic bits.
• This modulation technique enables advantages described herein, including reducing a ripple in a voltage produced by the wireless power receiver from the electromagnetic field during the communication and pause time periods.
• the specific components shown and described for the power transmitter 110 and the power receiving device 111 are presented for illustrative purposes only and not necessarily intended to limit the invention. Other components, or combinations or configurations thereof, can also be used, while remaining within the scope of the invention.
• the primary and secondary inductor coils (i.e. electromagnetic field coupling components) 112 and 113 could be capacitive devices, instead of inductive devices.
• Other component variations are possible for other embodiments.
• the power transmitter 110 in addition to the primary inductor coil 112, the power transmitter 110 generally includes a power conversion unit 114 and a communications and control unit (the control unit) 115.
• the power conversion unit 114 generally includes an AC to DC converter 116 and one or more power drivers 117.
• the control unit 115 generally includes a controller (e.g. a microcontroller or CPU) 118 and one or more voltage and current sensors (V/I sense) 1 19.
• the power conversion unit 114 generally receives electrical power from an external source, such as an AC power source, and generates a power signal (through the AC to DC converter 116 and drivers 117) that is applied to the primary inductor coil 112 to create the coupling electromagnetic field.
• the base frequency for the power signal, and the coupling electromagnetic field generated therefrom is typically in a range of about 100-200 KHz, but frequencies outside this range are known and acceptable in the invention.
• the WPC standard for example, calls for an operational frequency in the 110-205 KHz range.
• the sensors 119 in the control unit 115 generally detect changes in the coupling electromagnetic field. Such changes may indicate the presence or absence of the power receiving device 111 within the
• Such communications generally arrive in packets, and various types of communication packets may be used. These may include, but are not limited to, identification and authentication packets, error packets, control packets, end power packets, and power usage packets.
• the controller 118 interprets the communication packets and, in response, determines how to set the level of the power signal produced by the power conversion unit 114.
• the power receiving device 111 generally maintains full control over the power transfer using the communication packets.
• the WPC standard and the bq500110 data sheet describe other acceptable, allowable or optional features for the power transmitter 110.
• the power receiving device 111 in addition to the secondary inductor coil 113, the power receiving device 111 generally includes a power pick-up unit 120, a communication and control unit 121 and a load 122.
• the load 122 generally represents a rechargeable battery 123 and/or device circuitry 124 for performing the primary functions of the power receiving device 111.
• the power pick-up unit 120 generally includes a rectification circuitry 125, a voltage regulator (e.g. a low dropout regulator, a switch mode regulator or other voltage conditioning or output disconnect circuitry) 126 and a modulator 127.
• the communication and control unit 121 generally includes a controller (e.g. a microcontroller or CPU) 128, a communication modulation signal generator (Comm.
• the Comm. Mod. 129 and the Pause Mod. 130 generally represent components, some of which may be shared, for generating an appropriate modulation signal by the communication and control unit 121 during the communication time periods and the intervening pause time periods.)
• the secondary inductor coil 113 generates an AC current and voltage from the coupling electromagnetic field.
• the AC current and voltage is rectified to a DC current and voltage (e.g. on line 131) by the rectification circuitry 125.
• the modulator 127 receives a portion of the DC current (e.g. on line 132) in order to modulate the rectified voltage as needed during the communication time periods and the intervening pause time periods.
• the voltage regulator 126 uses the rectified voltage to generate a substantially constant or stable supply voltage for the load 122 (e.g. on line 133).
• the rectification circuitry 125 also preferably provides power (e.g. on line 134) to the communication and control unit 121. Additionally, the communication and control unit 121 preferably receives a sense signal (e.g. on dashed line 135) indicative of the voltage and/or current of the rectified voltage on line 131. Furthermore, the communication and control unit 121 preferably receives one or more feedback signal (e.g. on line 136) indicative of the power usage of the load 122 or the state of charge of the battery 123 or other appropriate status data. (The communication and control unit 121 also typically generates control signals on lines 137 and 138 to control the voltage regulator 126 and the load 122, respectively, as necessary.)
• the communication and control unit 121 Based on the sense signal (line 135) and the feedback signal (line 136), the communication and control unit 121 (e.g. via the controller 128) generally determines the commands and/or data to be transmitted to the power transmitter 110 for the power transmitter 110 to make any needed adjustments to its power output level. Through the Comm. Mod. 129, the communication and control unit 121 periodically generates a differential bi-phase encoded modulation signal representative of the logic bits of the command or data to be transmitted to the power transmitter 110. The differential bi-phase encoded modulation signal is provided to the modulator 127 (e.g.
• the modulator 127 can modulate the rectified voltage level (line 131) in a manner representative of the logic bits during the communication time periods, so the resulting electromagnetic field alterations occur in a manner that leads to the power transmitter 110 detecting the logic bits.
• the pause time periods however, the
• the communication and control unit 121 (through the Pause Mod. 130) generates a second non- encoded modulation signal, which is provided to the modulator 127 on line 139, so the modulator 127 can modulate the rectified voltage (line 131) to alter the electromagnetic field in a manner that the power transmitter 110 cannot detect as the logic bits.
• the modulation during the pause time periods is preferably substantially more rapid, or at a higher frequency, than the modulation during the
• the modulation frequency is preferably outside the audible range. A factor of five difference from the communication frequency and the base frequency is typically appropriate.
• the communication frequency for wireless power transmission is commonly within the range of 200 Hz to 10 kHz, and the base frequency is commonly 100-200 kHz. (Communication and base frequencies outside these ranges are also possible.) Therefore, the rapid modulation frequency is preferably in a range of about 1-50 kHz, depending on the communication and base frequencies.
• the communication frequency is about 2 kHz (i.e. the bit rate is about 2 kbps) and the base frequency is about 110-205 kHz.
• an appropriate rapid modulation frequency may thus have a lower limit of about 10 kHz (i.e. 5x of 2 kHz) and an upper limit of about 22-41 kHz (i.e. 5x less than 110-205 kHz).
• Other ranges for the rapid modulation frequency are also possible and generally may depend on the communication and base frequencies.
• Power transmitters typically filter out frequencies slightly higher than the communication frequency in their control unit (e.g. control unit 115), so the rapid modulation frequency cannot cause such power transmitters to erroneously detect a stream of logic bits in the changes to the electromagnetic field.
• Other modulation techniques that cannot result in the power transmitter 110 erroneously detecting logic bits during pause time periods are also within the scope of the invention.
• the design of the power pick-up unit 120 preferably coordinates the rectified voltage level (line 131) and the modulation thereof with the headroom necessary for efficient operation of the voltage regulator 126.
• the modulation of the rectified voltage during the pause time periods is preferably performed in a manner such that the average of the rectified voltage level during these time periods is about the same as the average of the rectified voltage level during the communication time periods.
• the headroom available for the voltage regulator 126 is, thus, relatively constant throughout the communication and pause time periods, compared to the prior art described above. Therefore, the voltage regulator 126 can be designed to operate with very little excess headroom.
• the efficiency of the voltage regulator 126 depends on the ratio of its voltage output to its voltage input, this efficiency can be maximized by minimizing the difference between the average rectified voltage levels during the communication and pause time periods, thereby minimizing any excess headroom of the voltage regulator 126 during any portion of its operation.
• circuitry 140 and 141 Two examples of circuitry 140 and 141 that are acceptable for performing the modulation with the secondary inductor coil 113, the rectification circuit 125 and the modulator 127 are shown in Figs. 5 and 6, respectively.
• the example circuitries 140 and 141 are shown for illustrative purposes only and are not necessarily intended to limit the scope of the invention. Instead, other circuitries for performing the modulation are also within the scope of the invention. Additionally, the invention is not limited to the exact components or connection schemes shown in Figs. 5 and 6.
• the example circuitry 140 of Fig. 5 generally includes the secondary inductor coil
• the resonant capacitor 147 and the secondary inductor coil 113 generally make up the resonant circuit for generating the AC current and voltage when the secondary inductor coil 113 is in the presence of the electromagnetic field generated by the power transmitter 110.
• the rectifier 142 rectifies the AC current and voltage into a DC current and voltage.
• the filter capacitor 148 performs an initial filtering to partially smooth out the rectified voltage, which still ripples at about the frequency of the electromagnetic field.
• the modulation transistor 150 receives the modulation signal (e.g.
• the modulation resistor 149 to and from the rectifier 142, thereby changing or modulating the load.
• the changing load alters the level of the rectified voltage and the resonant frequency of the electromagnetically coupled primary and secondary inductor coils 112 and 113.
• the change in the resonant frequency alters the electromagnetic field, which changes the voltages or currents in the power transmitter 110.
• the sensors 119 detect the changes in the voltages or currents in the power transmitter 110 as the intended logic bits.
• the modulation is performed at the more rapid frequency during the pause time periods, the sensors 119 cannot detect the changes in the voltages or currents in the power transmitter 110.
• the example circuitry 141 of Fig. 6 generally includes the secondary inductor coil
• the resonant capacitor 156 and the secondary inductor coil 113 generally make up the resonant circuit for generating the AC current and voltage when the secondary inductor coil 113 is in the presence of the electromagnetic field generated by the power transmitter 110.
• the rectifier 151 rectifies the AC current and voltage into a DC current and voltage.
• the filter capacitor 157 performs an initial filtering to partially smooth out the rectified voltage, which still ripples at about the frequency of the electromagnetic field.
• the modulation transistors 160 and 161 receive the modulation signal (e.g. on line 139, see also Fig. 4) from the communication and control unit 121 and, in response, connects and disconnects the modulation capacitors 158 and 159 to and from the secondary inductor coil 113 (between the secondary inductor coil 113 and the rectifier 151), thereby changing or modulating the load.
• the changing load alters the level of the rectified voltage and the resonant frequency of the electromagnetically coupled primary and secondary inductor coils 112 and 113.
• the system resonant frequency is usually lower compared to the case when the modulation capacitors 158 and 159 are decoupled.
• the change in the resonant frequency alters the electromagnetic field, which changes the voltages or currents in the power transmitter 110.
• the sensors 119 detect the changes in the voltages or currents in the power transmitter 110 as the intended logic bits.
• the modulation is performed at the more rapid frequency during the pause time periods, the sensors 119 cannot detect the changes in the voltages or currents in the power transmitter 110.
• Figs. 7, 8 and 9 show graphs generated via a simulation of a circuit incorporating an embodiment of the invention.
• Graph 162 of Fig. 7 is a simplified graph of an example modulation signal that may be produced by the communication and control unit 121 on line 139 (Figs. 4, 5 and 6).
• the modulation signal graph 162 generally includes two communication time periods 163 and two pause time periods 164.
• the relative lengths shown for the communication and pause time periods 163 and 164 and the time scale (x-axis) are for illustrative purposes only and are not intended to limit the scope of the invention. Other lengths for the communication and pause time periods 163 and 164 and other time scales are within the scope of the invention.
• WPC-compliant wireless power transmission systems or systems in accordance with the bq500110 data sheet or the bq51010, bq51011 and bq51013 data sheet may transmit communication packets from the power receiving device 111 to the power transmitter 110 every 250ms during relatively steady state operating conditions, but if a large transient occurs, the feedback to the power transmitter 110 may speed up to every 30-32ms in order to converge on an operating point in less time.
• the modulation signal graph 162 alternates between high and low values that represent a differential bi-phase encoded bit stream similar to the prior art example described above with reference to Fig. 1. (The logic bits represented by the communication portions of the modulation signal graph 162 are not intended to correspond to any particular command or data that the power receiving device 111 might send to the power transmitter 110.)
• the modulation signal graph 162 alternates much more rapidly between the high and low values than it does during the communication time periods 163.
• Graph 165 of Fig. 8 is a simplified graph of an example rectified voltage (e.g. on line 131, Fig. 4) as might be produced by the rectification circuit 125 resulting from modulation by the modulator 127 as activated by the modulation signal (graph 162) shown in Fig. 7.
• the rectified voltage graph 165 generally shows the two communication time periods 163 and the two pause time periods 164 corresponding to those shown in Fig. 7.
• the rectified voltage level is modulated between high and low levels according to the modulation signal (graph 162).
• the modulation component e.g. the modulation resistor 149 of Fig. 5 or the modulation capacitors 158 and 159 of Fig.
• the rectified voltage level is modulated between the high and low levels at such a rapid rate that the rectified voltage doesn't always have time to reach these levels before being driven back in the opposite direction.
• the rectified voltage level may be said to change within some range between the high and low levels in some embodiments.
• the rectified voltage graph 165 may be compared to the prior art rectified voltage graph 105 of Fig. 2. Both graphs 105 and 165 are drawn at approximately the same vertical and horizontal scales. Whereas the prior art rectified voltage graph 105 remains at the high level during the pause time periods 107, the rectified voltage graph 165 fluctuates around approximately a midpoint between the high and low levels.
• Graph 166 of Fig. 9 is a simplified graph of an approximate average of the rectified voltage shown in Fig. 8 for each of the communication and pause time periods 163 and 164.
• the average rectified voltage graph 166 may be compared to the prior art average rectified voltage graph 108 of Fig. 3. Both graphs 108 and 166 are drawn at approximately the same vertical and horizontal scales.
• the difference between the average rectified voltage of the communication time periods 163 and the average rectified voltage of the pause time periods 164 of graph 166 in Fig. 9 is significantly smaller than the difference between the prior art average rectified voltage levels of the communication and pause time periods 106 and 107 of the graph 108 in Fig. 3.
• the filtering capacitors 148 and 157 of Figs. 5 and 6 had to be relatively large to properly handle the wide variation in the average rectified voltage level (e.g. graph 108, Fig. 3) over the relatively long time duration of a cycle of any two consecutive communication and pause time periods 106 and 107.
• the filtering capacitors 148 and 157 of Figs. 5 and 6 can be significantly smaller, and thus cheaper, than those of the prior art.
• Additional embodiments may bring the averages of the rectified voltage during the communication and pause time periods 163 and 164 even closer together than described above.
• the voltage level of the average rectified voltage during the pause time periods can be set to a desired level.
• the duty cycle of the modulation signal 162 during the pause time periods 164 for the example embodiment shown in Figs. 7-10 is 50%.
• the prior art example of Figs. 1, 2 and 3 generally represents a case having a duty cycle of 0%>.
• the differential bi-phase encoding scheme used for the modulation signal 162 during the communication time periods 163 is generally intended to result in the average voltage level of the rectified voltage 165 during these times being at about a midpoint between the high and low states thereof.
• the 50%> duty cycle during the pause time periods 164 generally results in the average voltage level of the rectified voltage 165 being at about a midpoint between the high and low points during these time periods.
• the rectified voltage 165 is preferably modulated relatively rapidly during the pause time periods 164, the rectified voltage
• circuit characteristics may skew the high and low points of the rectified voltage 165 during the pause time periods 164 either up or down relative to the high and low states during the communication time periods 163.
• the average rectified voltage 166 (Figs. 9 and 10) is similarly skewed during the pause time periods 164.
• Fig. 11 shows a rectified voltage graph 167 generated in a simulation in which the modulation signal (not shown) during communication time periods 168 encodes the same bit stream as the modulation signals 104 and 162 of Figs. 1 and 7.
• the modulation signal fluctuates at about the same frequency at which the modulation signal 162 fluctuates, but with about a 60% duty cycle instead of a 50% duty cycle.
• the rectified voltage 167 within the communication time periods 168 is about the same as the rectified voltage 165 of Fig. 8.
• the rectified voltage 167 is slightly lower than the rectified voltage 165 of Fig. 8. The difference is barely noticeable at the scale of Figs. 8 and 1 1.
• Fig. 12 shows an average rectified voltage graph 170 for the rectified voltage 167 at about the same finer vertical scale as for the average rectified voltage 166 of Fig. 10. At this scale, it can be seen that the average rectified voltage graph 170 during the pause time periods 169 is closer to the average rectified voltage graph 170 during the communication time periods 168 than is the case for the 50% duty cycle example of Fig. 10.
• Other embodiments may set or adjust the duty cycle of the modulation signal to any appropriate value to bring the average rectified voltage during the pause time periods close to the average rectified voltage during the communication time periods, thereby minimizing the difference between these averages.
• the above described advantages of the invention may, thus, be enhanced with this technique.
• the headroom that the voltage regulator 126 must operate under, for example, may be minimized, thereby potentially maximizing the efficiency of the voltage regulator 126.

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