Wireless power transfer

1. A power transmitter comprising:

a transmitter coil, wherein the transmitter coil is configured to generate a power transfer signal;

a driver circuit, wherein the driver circuit is configured to generate a drive signal for the transmitter coil so as to generate the power transfer signal;

a foreign object detector,

wherein the foreign object detector is configured to perform a foreign object detection operation,

wherein the foreign object detection operation is configured to detect a presence of a foreign object in response to a property of the drive signal;

a communicator circuit,

wherein the communicator circuit is configured to receive a power operating point indication from a power receiver during a power transfer phase,

wherein the power operating point indication represents a load power for a load of the power receiver; and

an adapter circuit,

wherein the adapter circuit is configured to adapt the foreign object detection operation by calibrating a detection criterion for detecting the foreign object during the power transfer phase in response to the power operating point indication,

wherein the power operating point indication indicates a change in the load power meeting a power operating point criterion, and wherein the power operating point criterion comprises a change in the load power exceeding a threshold value.

2. The power transmitter of claim 1 , wherein the power operating point indication is indicative of a future change in the load power.

3. The power transmitter of claim 1 ,

wherein the load power indicated by the power operating point indication is a target load power,

wherein the adapter circuit is configured to initiate a calibration process in response to the power operating point indication indicating the change in the target load power meeting the power operating point criterion, and

wherein the calibration process determines a calibration parameter for the foreign object detection operation in response to a measurement of the property of the drive signal.

4. The power transmitter of claim 1 , wherein the load power indicated by the power operating point indication is a target load power,

wherein the adapter circuit is configured to bias the foreign object detection operation towards no detection of a foreign object for a time interval in response to the power operating point indication indicating the change in the target load power meets the power operating point criterion.

5. The power transmitter of claim 1 ,

wherein the load power indicated by the power operating point indication is a target load power,

wherein the adapter circuit is configured to adapt the foreign object detection operation to not detect a foreign object for a time interval in response to the power operating point indication indicating the change in the target load power meets the power operating point criterion.

6. The power transmitter of claim 1 , wherein the power operating point indication is independent of a current power extraction by the power receiver.

7. The power transmitter of claim 1 ,

wherein the power operating point indication is included in a power level message,

wherein the power level message indicates a power extracted from the power transfer signal by the power receiver.

8. The power transmitter of claim 1 ,

wherein the load power indicated by the power operating point indication is a target load power,

wherein the power operating point indication is an indication of whether a change in the target power level meets the power operating point criterion.

9. The power transmitter of claim 1 ,

wherein the power operating point indication comprises a single one bit flag that indicates a change in the power operating point has occurred, and

wherein the adapter circuit is configured to perform a calibration of the foreign object detector in response to the power operating point indication.

10. The power transmitter of claim 1 ,

wherein the threshold value is a rate of change of power, and wherein the power operating point indication indicates that the power operating point criterion has been met when a measured rate of change in power level exceeds the threshold value.

11. A method of operation for a power transmitter, wherein the power transmitter is configured to provide power to a power receiver, the method comprising:

generating a drive signal for a transmitter coil such that the transmitter coil generates a power transfer signal;

executing a foreign object detection operation to detect a presence of a foreign object in response to a property of the drive signal;

receiving a power operating point indication from the power receiver during a power transfer phase, wherein the power operating point indication represents a load power for a load of the power receiver; and

adapting the foreign object detection operation by calibrating a detection criterion for detecting the foreign object during the power transfer phase in response to the power operating point indication,

wherein the power operating point indication indicates a change in the load power meeting a power operating point criterion,

wherein the power operating point criterion comprises a change in the load power exceeding a threshold value.

12. The method of claim 11 , wherein the power operating point indication is indicative of a future change in the load power.

13. The method of claim 11 , wherein the load power indicated by the power operating point indication is a target load power,

the method further comprising calibrating the transmitter in response to the power operating point indication indicating the change in the target load power meeting the power operating point criterion, wherein the calibrating comprises determining a calibration parameter for the foreign object detection operation in response to a measurement of the property of the drive signal.

14. The method of claim 11 ,

wherein the power operating point indication comprises a single one bit indication that indicates a change in the power operating point has occurred, and

wherein the adapter circuit is configured to perform a calibration of the foreign object detector in response to the power operating point indication.

15. The method of claim 11 ,

wherein the threshold value is a rate of change of power, and wherein the power operating point indication indicates that the power operating point criterion has been met when a measured rate of change in power level exceeds the threshold value.

16. A non-transitory computer readable medium having stored thereon instructions that when executed by processing circuitry of a wireless power transmitter cause the wireless power transmitter to:

generate a drive signal for a transmitter coil such that the transmitter coil generates a power transfer signal;

execute a foreign object detection operation to detect a presence of a foreign object in response to a property of the drive signal;

receive a power operating point indication from the power receiver during a power transfer phase, wherein the power operating point indication represents a load power for a load of the power receiver; and

adapt the foreign object detection operation by calibrating a detection criterion for detecting the foreign object during the power transfer phase in response to the power operating point indication,

wherein the power operating point indication indicates a change in the load power meeting a power operating point criterion, and

wherein the power operating point criterion comprises a change in the load power exceeding a threshold value.

17. The non-transitory computer readable medium of claim 16 , wherein the power operating point indication is indicative of a future change in the load power.

18. The non-transitory computer readable medium of claim 16 , wherein the load power indicated by the power operating point indication is a target load power, the instructions further comprising instructions that, when executed by the processing circuitry, cause the wireless power transmitter to determine a calibration parameter for the foreign object detection operation in response to a measurement of the property of the drive signal.

19. The non-transitory computer readable medium of claim 16 ,

wherein the power operating point indication comprises a single one bit flag that indicates a change in the power operating point has occurred, and

wherein instructions, when executed by the processing circuitry, cause the wireless power transmitter to perform a calibration of a foreign object detector in response to the power operating point indication.

20. The non-transitory computer readable medium of claim 16 ,

wherein the power operating point indication indicates that that the power operating point criterion has been met when a charging mode of the receiver has changed.