Adaptive rectifier and method of operation

1. A wireless power transfer system, comprising:

a wireless power receiver including: a rectifier including switches and a rectifier input having first and second rectifier input nodes; a secondary coil having a first terminal coupled to the first rectifier input node, and having a second terminal coupled to the second rectifier input node; and control circuitry to control the switches, including varying states of the switches to ensure a complex impedance at the rectifier input by shifting a phase of a voltage between the first and second rectifier input nodes relative to a phase of the secondary coil.

2. The wireless power transfer system of claim 1 , wherein the control circuitry is configured to control the switches to ensure the complex impedance with variable phase into the rectifier.

3. The wireless power transfer system of claim 2 , wherein the control circuitry is configured to control an output pulse width for control of a first parameter and to control a phase of the output pulse to adjust a second parameter.

4. The wireless power transfer system of claim 3 , wherein the first parameter is output current to a load, and the second parameter is efficiency of the wireless power receiver.

5. The wireless power transfer system of claim 3 , wherein the first parameter is voltage to a load, and the second parameter is efficiency of the wireless power receiver.

6. The wireless power transfer system of claim 2 , wherein the control circuitry is configured to control a phase of the complex impedance at the rectifier input, so that a resistance of the rectifier input is negative.

7. The wireless power transfer system of claim 6 , wherein the wireless power receiver is configured to transfer power to a wireless power transmitter when the resistance of the input to the rectifier is negative.

8. The wireless power transfer system of claim 1 , further comprising:

a wireless power transmitter configured to: sense current phase changes resulting from reflected impedance of the rectifier in the wireless power receiver; and control a parameter in the wireless power transmitter in response to the reflected impedance of the rectifier in the wireless power receiver.

9. The wireless power transfer system of claim 1 , wherein the complex impedance is a variable impedance, and the wireless power receiver is configured to encode information in the variable impedance at the rectifier input.

10. The wireless power transfer system of claim 9 , further comprising:

a wireless power transmitter configured to: sense changes in the variable impedance reflected from the wireless power receiver; and decode information encoded in the changes.

11. The wireless power transfer system of claim 1 , wherein the control circuitry is configured to control the switches in the rectifier to at least partially discharge a voltage at an output of the rectifier, for preventing a magnitude of that voltage from exceeding a maximum value.

12. A method of controlling a wireless power transfer system, the method comprising:

controlling, by control circuitry in a wireless power receiver, switches in a rectifier that includes a rectifier input having first and second rectifier input nodes, wherein controlling the switches includes varying states of the switches to ensure a complex impedance at the rectifier input by shifting a phase of a voltage between the first and second rectifier input nodes relative to a phase of a secondary coil, the secondary coil having a first terminal coupled to the first rectifier input node, and having a second terminal coupled to the second rectifier input node.

13. The method of claim 12 , further comprising:

controlling, by the control circuitry in the wireless power receiver, the switches in the rectifier to control two different operating parameters of the wireless receiver.

14. The method of claim 12 , further comprising:

controlling, by the control circuitry in the wireless power receiver, the switches in the rectifier to control a phase of the complex impedance at the rectifier input, so that a resistance of the rectifier input is negative.

15. The method of claim 14 , further comprising:

wirelessly transferring, by the wireless power receiver, power to a wireless power transmitter.

16. The method of claim 12 , wherein the complex impedance is a variable impedance, and the method further comprises:

encoding, by the wireless power receiver, information in the variable impedance at the rectifier input.

17. The method of claim 16 , further comprising:

sensing, by a wireless power transmitter, changes in the variable impedance reflected from the wireless power receiver; and

decoding, by the wireless power transmitter, information encoded in the changes.

18. The method of claim 12 , further comprising:

controlling, by the control circuitry in the wireless power receiver, the switches in the rectifier to at least partially discharge a voltage at an output of the rectifier, for preventing a magnitude of that voltage from exceeding a maximum value.