Method and apparatus for tuning a resistance and reactance of a wireless power transmitter testing unit

1. An apparatus for testing an impedance range of a wireless power transmitter, comprising:

an adjustable impedance circuit configurable to be connected to a power source;

a transformer coupled to the adjustable impedance circuit;

a sensing circuit configured to sense a parameter indicative of a parasitic impedance of the adjustable impedance circuit; and

a driver circuit configured to drive the transformer with a signal based on the sensed parameter that causes the transformer to apply a first voltage to the adjustable impedance circuit, the first voltage having a substantially same amplitude as a voltage drop caused by the parasitic impedance and being out of phase with the voltage drop.

2. The apparatus of claim 1 , wherein the sensed parameter is at least one of a current circulating in the adjustable impedance circuit or a voltage across at least a portion of the adjustable impedance circuit.

3. The apparatus of claim 1 , wherein the parasitic impedance has a parasitic resistance, and wherein the transformer is configured to add a negative resistance to the adjustable impedance circuit by applying the first voltage to the adjustable impedance circuit, the negative resistance being substantially equal in magnitude to the parasitic resistance.

4. The apparatus of claim 1 , wherein the transformer is coupled to a balance point of the adjustable impedance circuit.

5. The apparatus of claim 4 , wherein the balance point comprises a node within the adjustable impedance circuit where a node voltage is substantially half of a voltage across the power supply.

6. The apparatus of claim 1 , further comprising a phase-shift circuit configured to shift a phase of the sensed parameter and provide the phase-shifted sensed parameter to the driver circuit.

7. The apparatus of claim 6 , wherein the phase-shift circuit is configured to shift the phase of the sensed parameter until the first voltage injected into the adjustable impedance circuit is 180° out of phase with the voltage drop.

8. The apparatus of claim 1 , wherein the sensing circuit comprises at least one of a current sense transformer or a differential amplifier.

9. The apparatus of claim 1 , wherein the adjustable impedance circuit is configurable to present an adjustable impedance to a wireless power transmit circuit of the wireless power transmitter.

10. A method for testing an impedance range of a wireless power transmitter, comprising:

sensing a parameter indicative of a parasitic impedance of an adjustable impedance circuit configurable to be connected to a power source, and

driving a transformer coupled to the adjustable impedance circuit with a signal based on the sensed parameter that causes the transformer to apply a first voltage to the adjustable impedance circuit, the first voltage having a substantially same amplitude as a voltage drop caused by the parasitic impedance and being out of phase with the voltage drop.

11. The method of claim 10 , wherein the sensed parameter is at least one of a current circulating in the adjustable impedance circuit or a voltage across at least a portion of the adjustable impedance circuit.

12. The method of claim 10 , wherein the parasitic impedance has a parasitic resistance and the method further comprises providing a negative resistance to the adjustable impedance circuit by applying the first voltage to the adjustable impedance circuit, the negative resistance being substantially equal in magnitude to the parasitic resistance.

13. The method of claim 12 , wherein the first voltage is applied to a balance point of the adjustable impedance circuit, the balance point having node voltage that is substantially half of a voltage across the power supply.

14. The method of claim 10 , further comprising shifting a phase of the sensed parameter and providing the phase-shifted sensed parameter to a driver circuit for driving the transformer.

15. The method of claim 14 , further comprising shifting the phase of the sensed parameter until the first voltage applied to the adjustable impedance circuit is 180° out of phase with the voltage drop.

16. The method of claim 10 , further comprising presenting an adjustable impedance to a wireless power transmit circuit of the wireless power transmitter.

17. An apparatus for testing an impedance range of a wireless power transmitter, comprising:

means for providing an adjustable impedance to a power source;

means for sensing a parameter indicative of a parasitic impedance of the means for providing the adjustable impedance; and

means for applying a first voltage to the means for providing the adjustable impedance based on the sensed parameter, the first voltage having a substantially same amplitude as a voltage drop caused by the parasitic impedance and being out of phase with the voltage drop.

18. The apparatus of claim 17 , wherein the parasitic impedance has a parasitic resistance, the apparatus further comprising means for adding a negative resistance to the means for providing the adjustable impedance by applying the first voltage to the means for providing the adjustable impedance, the negative resistance being substantially equal in magnitude to the parasitic resistance.

19. The apparatus of claim 17 , further comprising means for shifting a phase of the sensed parameter and providing the phase-shifted sensed parameter to the means for applying the first voltage to the means for providing the adjustable impedance.

20. The apparatus of claim 19 , wherein the means for shifting the phase of the sensed parameter is configured to shift the phase of the sensed parameter until the first voltage is 180° out of phase with the voltage drop.