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A communication system that uses keyed modulation to encode fixed frequency communications on a variable frequency power transmission signal in which a single communication bit is represented by a plurality of modulations. To provide a fixed communication rate, the number of modulations associated w

A communication system that uses keyed modulation to encode fixed frequency communications on a variable frequency power transmission signal in which a single communication bit is represented by a plurality of modulations. To provide a fixed communication rate, the number of modulations associated with each bit is dynamic varying as a function of the ratio of the communication frequency to the carrier signal frequency. In one embodiment, the present invention provides dynamic phase-shift-keyed modulation in which communications are generated by toggling a load at a rate that is a fraction of the power transfer frequency. In another embodiment, the present invention provides communication by toggling a load in the communication transmitter at a rate that is phase locked and at a harmonic of the power transfer frequency. In yet another embodiment, the present invention provides frequency-shift-keyed modulation, including, for example, modulation at one of two different frequencies.

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1. A method of communicating data between a remote device and an inductive power supply using keyed modulation, said method comprising: receiving inductive power via a variable frequency power transmission signal from the inductive power supply;encoding a data stream of bits into a fixed frequency c

1. A method of communicating data between a remote device and an inductive power supply using keyed modulation, said method comprising: receiving inductive power via a variable frequency power transmission signal from the inductive power supply;encoding a data stream of bits into a fixed frequency communication signal;modulating the fixed frequency communication signal on the variable frequency power transmission signal by toggling a load of a communication transmitter, wherein each bit of the data stream is represented by a plurality of modulations on the variable frequency power transmission signal; anddecoding the data stream from the variable frequency power transmission signal by timeslicing the variable frequency power transmission signal and comparing a DC offset between two time slices. 2. The method as claimed in claim 1 wherein the communication transmitter is configured to modulate the load, and wherein said modulating includes toggling the load in the communication transmitter at a rate that is a fraction of the variable frequency power transmission signal. 3. The method as claimed in claim 2 wherein the rate is one-half the variable frequency power transmission signal. 4. The method as claimed in claim 2 wherein said modulating includes toggling the load to increase a magnitude of every other waveform of the variable frequency power transmission signal. 5. The method as claimed in claim 4 wherein said modulating includes toggling the load on every even waveform or every odd waveform. 6. The method as claimed in claim 2 wherein said modulating includes toggling the load to increase the magnitude of the peak or the trough of every other waveform of the variable frequency power transmission signal. 7. The method as claimed in claim 1 wherein said modulating includes producing a modulator control signal formed by exclusive OR-ing (a) a modulation clock that is operating at an even integer fraction of the variable frequency power transmission signal and (b) the fixed frequency communication signal, wherein the variable frequency power transmission signal is modulated according to said modulator control signal. 8. The method as claimed in claim 1 wherein the communication transmitter is configured to modulate the load at a modulation rate that is phase locked at a harmonic of the variable frequency power transmission signal. 9. The method as claimed in claim 8 wherein the rate is four times the variable frequency power transmission signal. 10. The method as claimed in claim 8 wherein said modulating includes: producing a first modulation control signal formed by exclusive OR-ing (a) a modulation clock operating at the modulation rate and (b) the fixed frequency communication signal;producing a second modulation control signal formed by inverting the exclusive OR of (a) a modulation clock operating at the modulation rate and (b) the fixed frequency communication signal;toggling the modulation load according to the first modulation control signal during a positive half of the variable frequency power transmission signal; andtoggling the modulation load according to the second modulation control signal during a negative half of the variable frequency power transmission signal. 11. The method as claimed in claim 8 further comprising decoding the data stream from the variable frequency power transmission signal by timeslicing the variable frequency power transmission signal and identifying DC offsets among the time slices. 12. The method as claimed in claim 1 wherein the load includes at least one of a resistive element, a capacitive element, and an inductive element. 13. The method as claimed in claim 1 wherein the communication transmitter modulates the fixed frequency communication signal on the variable frequency power transmission signal such that communication inversion is avoided. 14. A system for transferring power to a remote device from an inductive power supply and for communicating data from the remote device to the inductive power supply, said system comprising: a power receiver adapted to receive a variable frequency power transmission signal;a controller adapted to encode a data stream of bits into a fixed frequency communication signal;a communication transmitter adapted to selectively toggle a load for modulating the fixed frequency communication signal on the variable frequency power transmission signal, wherein each bit of the data stream is represented by a plurality of modulations on the variable frequency power transmission signal; anda detector configured to decode the data stream from the variable frequency power transmission signal by timeslicing the variable frequency power transmission signal and comparing a DC offset between two time slices. 15. The system as claimed in claim 14 wherein the communication transmitter is configured to modulate the load, and wherein said modulating includes toggling the load in the communication transmitter at a rate that is a fraction of the variable frequency power transmission signal. 16. The system as claimed in claim 15 wherein the rate is one-half the variable frequency power transmission signal. 17. The system as claimed in claim 15 wherein the load is toggled to increase a magnitude of every other waveform of the variable frequency power transmission signal. 18. The system as claimed in claim 17 wherein said modulating includes toggling the load on every even waveform or every odd waveform. 19. The system as claimed in claim 15 wherein the load is toggled to increase the magnitude of the peak or the trough of every other waveform of the variable frequency power transmission signal. 20. The system as claimed in claim 14 wherein the modulating includes producing a modulator control signal formed by exclusive OR-ing (a) a modulation clock that is operating at an even integer fraction of the variable frequency power transmission signal and (b) the fixed frequency communication signal, wherein the variable frequency power transmission signal is modulated according to said modulator control signal. 21. The system as claimed in claim 14 wherein the communication transmitter is configured to modulate the load at a modulation rate that is phase locked at a harmonic of the variable frequency power transmission signal. 22. The system as claimed in claim 21 wherein the rate is four times the variable frequency power transmission signal. 23. The system as claimed in claim 21 wherein the modulating includes: producing a first modulation control signal formed by exclusive OR-ing (a) a modulation clock operating at the modulation rate and (b) the fixed frequency communication signal;producing a second modulation control signal formed by inverting the exclusive OR of (a) a modulation clock operating at the modulation rate and (b) the fixed frequency communication signal;toggling the modulation load according to the first modulation control signal during a positive half of the variable frequency power transmission signal; andtoggling the modulation load according to the second modulation control signal during a negative half of the variable frequency power transmission signal. 24. The system as claimed in claim 14 wherein the load includes at least one of a resistive element, a capacitive element, and an inductive element. 25. The system as claimed in claim 14 wherein the communication transmitter modulates the fixed frequency communication signal on the variable frequency power transmission signal such that communication inversion is avoided. 26. A system for transferring power to a remote device from an inductive power supply and for communicating data between the remote device and the inductive power supply using keyed modulation, said system comprising: a power receiver adapted to receive a variable frequency power transmission signal;a controller for encoding a data stream of bits in to a fixed frequency communication signal;a communication transmitter selectively toggling a load for modulating the fixed frequency communication signal on the variable frequency power transmission signal, wherein each bit of the data stream is represented by a plurality of modulations on the variable frequency power transmission signal; andan inductive power supply controller configured to decode the data stream from the variable frequency power transmission signal by timeslicing the variable frequency power transmission signal and comparing a DC offset between two time slices. 27. The system as claimed in claim 26 wherein said remote device includes said communication transmitter such that said remote device communicates data to the inductive power supply using keyed modulation, and wherein said inductive power supply includes detector circuitry for decoding the data stream from the variable frequency power transmission signal. 28. The system as claimed in claim 26 wherein said inductive power supply includes said communication transmitter such that said inductive power supply communicates data to the remote device using said keyed modulation, and wherein said remote device includes detector circuitry for decoding the data stream from the variable frequency power transmission signal. 29. The system as claimed in claim 26 wherein said communication transmitter is configured to modulate said load, and wherein the modulating includes toggling the load in the communication transmitter at a rate that is a fraction of the variable frequency power transmission signal. 30. The system as claimed in claim 29 wherein the rate is one-half the variable frequency power transmission signal. 31. The system as claimed in claim 29 wherein the load is toggled to increase a magnitude of every other waveform of the variable frequency power transmission signal. 32. The system as claimed in claim 30 wherein the load is toggled to increase the magnitude of the peak or the trough of every other waveform of the variable frequency power transmission signal. 33. The system as claimed in claim 32 wherein the modulating includes toggling the load on every even waveform or every odd waveform. 34. The system as claimed in claim 26 wherein the modulating includes producing a modulator control signal formed by exclusive OR-ing (a) a modulation clock that is operating at an even integer fraction of the variable frequency power transmission signal and (b) the fixed frequency communication signal, wherein the variable frequency power transmission signal is modulated according to said modulator control signal. 35. The system as claimed in claim 27 wherein the communication transmitter is configured to modulate the load at a modulation rate that is phase locked at a harmonic of the variable frequency power transmission signal. 36. The system as claimed in claim 35 wherein the rate is four times the variable frequency power transmission signal. 37. The system as claimed in claim 35 wherein said modulating includes: producing a first modulation control signal formed by exclusive OR-ing (a) a modulation clock operating at the modulation rate and (b) the fixed frequency communication signal;producing a second modulation control signal formed by inverting the exclusive OR of (a) a modulation clock operating at the modulation rate and (b) the fixed frequency communication signal;toggling the modulation load according to the first modulation control signal during a positive half of the variable frequency power transmission signal; andtoggling the modulation load according to the second modulation control signal during a negative half of the variable frequency power transmission signal. 38. The system as claimed in claim 35 further comprising an inductive power supply controller configured to decode the data stream from the variable frequency power transmission signal by timeslicing the variable frequency power transmission signal and identifying DC offsets among the time slices. 39. The system as claimed in claim 26 wherein the load includes at least one of a resistive element, a capacitive element, and an inductive element. 40. The system as claimed in claim 26 wherein the communication transmitter modulates the fixed frequency communication signal on the variable frequency power transmission signal such that communication inversion is avoided. 41. An inductive power supply for transferring inductive power to a remote device and for receiving data via backscatter modulation from the remote device, said inductive power supply comprising: a power transmitter for transmitting a variable frequency power transmission signal;a wireless communication receiver configured to detect modulation on the variable frequency power transmission signal, wherein the inductive power supply decodes a data stream from the variable frequency power transmission signal, and wherein each bit of the data stream is represented by a plurality of modulations on the variable frequency power transmission signal; andwherein the inductive power supply decodes the data stream by timeslicing the variable frequency power transmission signal and comparing a DC offset between two time slices. 42. The inductive power supply as claimed in claim 41 wherein the fixed frequency communication signal is a bi-phase encoded representation of the data stream. 43. The inductive power supply of claim 41 wherein the inductive power supply includes a detector circuit having a first amplifier chain and a second amplifier chain; said first amplifier chain averaging (a) a buffered copy of even cycles of the variable frequency power transmission signal and (b) an inverted buffered copy of odd cycles of the variable frequency power transmission signal;said second amplifier chain averaging (a) a buffered copy of odd cycles of the variable frequency power transmission signal and (b) an inverted buffered copy of even cycles of the variable frequency power transmission signal; andwherein in response to comparing the output of the first amplifier chain and the second amplifier chain, the detector circuit outputs a fixed frequency communication signal representative of the data stream. 44. The inductive power supply of claim 41 wherein the inductive power supply includes a first detector circuit having a first amplifier chain that detects peaks of a buffered copy of even cycles of the variable frequency power transmission signal and a second amplifier chain that detects peaks of a buffered copy of odd cycles of the variable frequency power transmission signal, and wherein in response to comparing the output of the first amplifier chain and the second amplifier chain, the first detector circuit outputs a first level shift output. 45. The inductive power supply of claim 44 wherein the inductive power supply includes a second detector circuit having a first trough amplifier chain that detects troughs of a buffered inverted copy of even cycles of the variable frequency power transmission signal and a second trough amplifier chain that detects troughs of a buffered inverted copy of odd cycles of the variable frequency power transmission signal, wherein in response to comparing the output of the first trough amplifier chain and the second trough amplifier chain, the second detector circuit outputs a second level shift output, andwherein the first level shift output and the second level shift output are combined to form a fixed frequency communication signal representative of the data stream. 46. The inductive power supply as claimed in claim 41 wherein the inductive power supply decodes the data stream from the variable frequency power transmission signal by passing the variable frequency power transmission signal through a frequency discriminator.