Systems and methods for bi-state impedance conversion in wireless power transfer

1. A wireless power transmitter comprising:

a transmit antenna configured to generate a field for wireless power transfer;

a first capacitor;

at least one switch configured to selectively connect the first capacitor in parallel with the transmit antenna in a first configuration and in series with the transmit antenna in a second configuration;

a second capacitor connected in parallel with the transmit antenna; and

a multi-tap transformer having a first turns-ratio and a second turns-ratio, the first turns-ratio being lower than the second turns-ratio,

the at least one switch further configured to select the first turns-ratio for the transformer in the first configuration and select the second turns-ratio for the transformer in the second configuration.

2. The wireless power transmitter of claim 1 , wherein the first capacitor is in series with the second capacitor in the first configuration and in parallel with the second capacitor in the second configuration.

3. The wireless power transmitter of claim 1 , further comprising a third capacitor in series with the at least one switch.

4. The wireless power transmitter of claim 3 , wherein the third capacitor is configured to compensate for an additional reactive loading present in the first configuration.

5. The wireless power transmitter of claim 3 , wherein the at least one switch comprises:

a first switch having a first terminal electrically coupled to a second terminal of the third capacitor and having a second terminal electrically coupled to a second terminal of the first capacitor and to a first terminal of the second capacitor; and

a second switch having a first terminal electrically coupled to a second terminal of a fourth capacitor and having a second terminal electrically coupled to a first terminal of the first capacitor and to a first terminal of the transmit antenna.

6. The wireless power transmitter of claim 5 , wherein the first switch is configured to connect the first capacitor in the first configuration.

7. The wireless power transmitter of claim 3 , the transformer having:

a first terminal electrically coupled to a first terminal of the third capacitor,

a second terminal electrically coupled to a first terminal of a fourth capacitor, and

a third terminal electrically coupled to a second terminal of the second capacitor and to a second terminal of the transmit antenna.

8. The wireless power transmitter of claim 1 , wherein the at least one switch is not part of a resonant path.

9. A method of transmitting wireless charging power in a wireless power transmitter, comprising:

generating, at a transmit antenna, a field for wireless power transfer;

selectively connecting a first capacitor, via at least one switch, in parallel with the transmit antenna in a first configuration and in series with the transmit antenna in a second configuration, the transmit antenna connected in parallel with a second capacitor;

selectively configuring a multi-tap transformer having a first turns-ratio and a second turns-ratio, the first turns-ratio being higher than the second turns-ratio, to operate with the first turns-ratio in the first configuration and to operate with the second turns-ratio in the second configuration via the at least one switch.

10. The method of claim 9 , wherein the first capacitor is in series with the second capacitor in the first configuration and in parallel with the second capacitor in the second configuration.

11. The method of claim 9 , wherein the wireless power transmitter comprises a third capacitor in series with the at least one switch.

12. The method of claim 11 , wherein the third capacitor is configured to compensate for an additional reactive loading present in the first configuration.

13. The method of claim 11 , wherein the at least one switch comprises:

a first switch having a first terminal electrically coupled to a second terminal of the third capacitor and having a second terminal electrically coupled to a second terminal of the first capacitor and to a first terminal of the second capacitor; and

a second switch having a first terminal electrically coupled to a second terminal of a fourth capacitor and having a second terminal electrically coupled to a first terminal of the first capacitor and to a first terminal of the transmit antenna.

14. The method of claim 13 , wherein the first switch is configured to connect the first capacitor in the first configuration.

15. The method of claim 11 , the transformer having:

a first terminal electrically coupled to a first terminal of the third capacitor,

a second terminal electrically coupled to a first terminal of a fourth capacitor, and

a third terminal electrically coupled to a second terminal of the second capacitor and to a second terminal of the transmit antenna.

16. The method of claim 9 , wherein the at least one switch is not part of a resonant path.

17. An apparatus for transmitting wireless charging power, comprising:

a first capacitor;

means for generating a field for wireless power transfer;

a second capacitor in parallel with the means for generating the field;

means for selectively connecting the first capacitor in parallel with the means for generating in a first configuration and in series with the means for generating in a second configuration; and

means for isolating having a first turns-ratio and a second turns-ratio, the first turns-ratio being higher than the second turns-ratio,

the means for selectively connecting configured to select the first turns-ratio for the means for isolating in the first configuration and select the second turns-ratio for the means for isolating in the second configuration.

18. The apparatus of claim 17 , wherein the means for selectively connecting connects the first capacitor in series with the second capacitor in the first configuration and in parallel with the second capacitor in the second configuration.

19. The apparatus of claim 17 , further comprising a third capacitor in series with the means for selectively connecting.

20. The apparatus of claim 19 , wherein the third capacitor is configured to compensate for an additional reactive loading present in the first configuration.

21. The apparatus of claim 19 , wherein the means for selectively connecting the first capacitor comprises:

a first means for selectively connecting having a first terminal electrically coupled to a second terminal of the third capacitor and having a second terminal electrically coupled to a second terminal of the first capacitor and to a first terminal of the second capacitor; and

a second means for selectively connecting having a first terminal electrically coupled to a second terminal of a fourth capacitor and having a second terminal electrically coupled to a first terminal of the first capacitor and to the means for generating.

22. The apparatus of claim 19 , wherein the means for isolating comprises:

a first terminal electrically coupled to a first terminal of the third capacitor,

a second terminal electrically coupled to a first terminal of a fourth capacitor, and

a third terminal electrically coupled to a second terminal of the second capacitor and to a second terminal of the means for generating.

23. The apparatus of claim 17 , wherein the means for selectively connecting is not part of a resonant path.

24. A non-transitory computer-readable medium comprising code that, when executed, causes an apparatus to:

generate, at a transmit antenna, a field for wireless power transfer;

selectively connect, via at least one switch, a first capacitor in parallel with the transmit antenna in a first configuration and in series with the transmit antenna in a second configuration, wherein the apparatus comprises a second capacitor in parallel with the transmit antenna; and

selectively configure, via the at least one switch, a multi-tap transformer having a first turns-ratio and a second turns-ratio, the first turns-ratio being higher than the second turns-ratio, to operate with the first turns-ratio in the first configuration and to operate with the second turns-ratio in the second configuration.

25. The medium of claim 24 , further comprising code that causes the apparatus to connect the first capacitor in series with the second capacitor in the first configuration and in parallel with the second capacitor in the second configuration.

26. The medium of claim 24 , wherein the apparatus comprises a third capacitor in series with the at least one switch.

27. The medium of claim 26 , wherein the third capacitor is configured to compensate for an additional reactive loading present in the first configuration.

28. The medium of claim 26 , wherein the apparatus comprises:

a first switch having a first terminal electrically coupled to a second terminal of the third capacitor and having a second terminal electrically coupled to a second terminal of the first capacitor and to a first terminal of the second capacitor; and

a second switch having a first terminal electrically coupled to a second terminal of a fourth capacitor and having a second terminal electrically coupled to a first terminal of the first capacitor and to a first terminal of the transmit antenna.

29. The medium of claim 26 , wherein the transformer comprises a multi-tap transformer having:

a first terminal electrically coupled to a first terminal of the third capacitor,

a second terminal electrically coupled to a first terminal of a fourth capacitor, and

a third terminal electrically coupled to a second terminal of the second capacitor and to a second terminal of the transmit antenna.

30. The medium of claim 24 , wherein the at least one switch not part of a resonant path.