Low power object detection in multi-coil wireless charging systems and related systems, methods, and devices

1. An apparatus, comprising:

a terminal to receive a measurement voltage potential at least partially responsive to a tank circuit signal at a tank circuit of a wireless power transmitter, the tank circuit including a plurality of transmit coils; and

a processing core to:

control provision of an alternating current (AC) signal to charge each of the plurality of transmit coils one at a time; and

select a transmit coil from the plurality of transmit coils to use to transmit wireless power to a receive coil of a wireless power receiver responsive to at least one of a resonant frequency and a Q-factor for each transmit coil of the plurality of transmit coils determined in absence of the AC signal after completion of provision of the AC signal to the tank circuit.

2. The apparatus of claim 1 , wherein the processing core to:

determine both the resonant frequency and the Q-factor of the tank circuit responsive to discharge of each selected transmit coil of the plurality of transmit coils in the absence of the AC signal after the completion of the provision of the AC signal to the tank circuit.

3. The apparatus of claim 1 , wherein the processing core to:

identify a lowest Q-factor transmit coil of the plurality of transmit coils associated with a lowest determined Q-factor value; and

identify a lowest resonant frequency transmit coil associated with a lowest determined resonant frequency value.

4. The apparatus of claim 3 , wherein the processing core to:

determine that a foreign object is located proximate to one or more transmit coils of the plurality of transmit coils at least partially responsive to:

a determination that the lowest determined Q-factor value is less than a threshold minimum Q-factor value; and

a determination that the lowest determined resonant frequency value is greater than an expected uncoupled resonant frequency.

5. The apparatus of claim 4 , wherein the processing core to:

enter a sleep mode responsive to a determination that the foreign object is located proximate to the one or more transmit coils.

6. The apparatus of claim 3 , wherein the processing core to:

determine that a proximity of the one or more transmit coils of the plurality of transmit coils is free of foreign objects and receive coils at least partially responsive to:

a determination that the lowest determined Q-factor value is not less than a threshold minimum Q-factor value; and

a determination that the lowest determined resonant frequency value is not less than a threshold minimum resonant frequency value.

7. The apparatus of claim 6 , wherein the processing core to:

enter a sleep mode at least partially responsive to a determination that the proximity of the one or more transmit coils is free of foreign objects and receive coils.

8. The apparatus of claim 3 , wherein the processing core to:

select the identified lowest Q-factor transmit coil to transmit the wireless power to the receive coil at least partially responsive to:

a determination that the lowest determined Q-factor value is less than a threshold minimum Q-factor value; and

a determination that the lowest determined resonant frequency value is not greater than an expected uncoupled resonant frequency.

9. The apparatus of claim 3 , wherein the processing core to:

select the lowest resonant frequency transmit coil to transmit the wireless power to the receive coil at least partially responsive to:

a determination that the lowest determined Q-factor value is not less than a threshold minimum Q-factor value; and

a determination that the lowest determined resonant frequency value is less than a threshold minimum resonant frequency value.

10. The apparatus of claim 3 , wherein the processing core to:

determine that the receive coil is proximate to the plurality of transmit coils at least partially responsive to each one of:

determinations that both the lowest determined Q-factor value is less than a threshold minimum Q-factor value and the lowest determined resonant frequency value is not greater than an expected uncoupled resonant frequency; and

determinations that both the lowest determined Q-factor value is not less than a threshold minimum Q-factor value and the lowest determined resonant frequency value is less than a threshold minimum resonant frequency value.

11. The apparatus of claim 1 , wherein a selected transmit coil to transmit the wireless power to the receive coil responsive to a selection, by the processing core, of the selected transmit coil.

12. The apparatus of claim 1 , wherein the processing core to:

determine the at least one of the resonant frequency and the Q-factor of the tank circuit based, at least in part, on identified peaks of the measurement voltage potential responsive to discharge of each selected transmit coil of the plurality of transmit coils in the absence of the AC signal after the completion of the provision of the AC signal to the tank circuit.

13. A method of operating a controller for a wireless power transmitter, the method comprising:

sampling a measurement voltage potential responsive to a tank circuit signal at a tank circuit of the wireless power transmitter, the tank circuit including a plurality of transmit coils;

provisioning an alternating current (AC) signal to charge each of the plurality of transmit coils one at a time; and

selecting a transmit coil from the plurality of transmit coils to use to transmit wireless power to a receive coil of a wireless power receiver responsive to at least one of a resonant frequency and a Q-factor for each transmit coil of the plurality of transmit coils determined in absence of the AC signal after completion of provision of the AC signal to the tank circuit.

14. The method of claim 13 , comprising:

determining the resonant frequency and the Q-factor of the tank circuit at least partially responsive to discharge of each selected transmit coil of the plurality of transmit coils in the absence of the AC signal after the completion of the provision of the AC signal to the tank circuit.

15. The method of claim 13 , comprising entering a sleep mode at least partially responsive to a determination that a foreign object is located proximate to one or more transmit coils of the plurality of transmit coils.

16. The method of claim 13 , comprising entering a sleep mode at least partially responsive to a determination that a proximity of one or more transmit coils of the plurality of transmit coils is free of foreign objects and receive coils.

17. The method of claim 13 , comprising controlling a selected transmit coil to transmit the wireless power to the receive coil at least partially responsive to the selecting of the selected transmit coil.

18. The method of claim 13 , comprising determining the at least one of the resonant frequency and the Q-factor of the tank circuit based, at least in part, on identified peaks of the measurement voltage potential responsive to discharge of each selected transmit coil of the plurality of transmit coils in the absence of the AC signal after the completion of the provision of the AC signal to the tank circuit.

19. The method of claim 18 , comprising identifying the identified peaks of the measurement voltage potential.

20. The method of claim 13 , wherein providing the AC signal to charge each of the plurality of transmit coils one at a time comprises controlling one or more coil select signals to select the plurality of transmit coils one at a time.