Methods and apparatuses for power control during backscatter modulation in wireless power receivers

1. A wireless power receiver, comprising:

a receive coil configured to generate an AC power signal responsive to a wireless power signal;

a rectifier configured to receive the AC power signal and generate a DC rectified power signal;

a power transistor operably coupled in a pass-transistor configuration and comprising an input node to receive the DC rectified power signal and an output node to provide an output power signal, the power transistor configured to operate in a substantially constant current mode during a communication period employing backscatter modulation on the receive coil;

a compensation current source coupled to the output node of the power transistor and configured to maintain a substantially constant voltage on the output power signal by adjusting a current through the compensation current source; and

a control logic coupled to the output node of the power transistor and configured to enable the compensation current source during the communication period.

2. The wireless power receiver of claim 1 , further comprising an amplifier operably coupled to the output power signal and configured to adjust the current through the compensation current source responsive to a voltage of the output power signal.

3. The wireless power receiver of claim 1 , wherein the control logic is further configured to:

sample a voltage level of the output power signal prior to the communication period; and control the current through the compensation current source to maintain a voltage of the output power signal substantially near the sampled voltage.

4. The wireless power receiver of claim 1 , wherein the control logic is further configured to control the current through the compensation current source to maintain a voltage of the output power signal substantially near a predetermined voltage.

5. The wireless power receiver of claim 4 , further comprising:

a power management device configured to control supply of power for a wireless power enabled apparatus from the output power signal, a battery, or a combination thereof; and

wherein the control logic is further configured to control the current through the compensation current source to maintain a voltage of the output power signal to a level that triggers the power management device to supply the power for the wireless power enabled apparatus only from the battery.

6. The wireless power receiver of claim 1 , further comprising a variable load operably coupled to the output power signal wherein the compensation current source maintains the substantially constant voltage on the output power signal during fluctuations in the variable load occurring during the communication period.

7. A method of operating a receiver side of a wireless power transfer system, the method comprising:

generating an AC power signal responsive to a wireless power signal exciting a receive coil at a resonant frequency;

rectifying the AC power signal to generate a DC rectified power signal;

generating, by a power transistor from the DC rectified power signal, at an output node of the power transistor, an output power signal at a substantially constant current during a communication period employing backscatter modulation on the receive coil; and

maintaining a substantially constant voltage on the output power signal by adjusting a current through a compensation current source, coupled to the output node of the power transistor, during the communication period.

8. The method of claim 7 , further comprising adjusting the current through the compensation current source responsive to a voltage of the output power signal.

9. The method of claim 7 , further comprising:

sampling a voltage level of the output power signal prior to the communication period; and

controlling the current through the compensation current source to maintain a voltage of the output power signal substantially near the sampled voltage.

10. The method of claim 7 , further comprising controlling the current through the compensation current source to maintain a voltage of the output power signal substantially near a predetermined voltage.

11. The method of claim 7 , further comprising maintaining the substantially constant voltage on the output power signal during fluctuations in a variable load operably coupled to the output power signal, the fluctuations occurring during the communication period.

12. The method of claim 11 , wherein the fluctuations in the variable load are due to at least one of a battery of an electronic device and system components of the electronic device.

13. A wireless power enabled apparatus, comprising:

a wireless power receiver, including:

a receive coil configured to generate an AC power signal responsive to a wireless power signal;

a rectifier configured to receive the AC power signal and generate a DC rectified power signal; and

a power transistor operably coupled in a pass-transistor configuration and comprising an input node to receive the DC rectified power signal and an output node to provide an output power signal, the power transistor configured to operate in a substantially constant current mode during a communication period employing backscatter modulation on the receive coil; and

a compensation current source coupled to the output node of the power transistor and configured to maintain a substantially constant voltage on the output power signal by adjusting a current through the compensation current source during the communication period.

14. The wireless power enabled apparatus of claim 13 , further comprising an amplifier operably coupled to the output power signal and configured to adjust the current through the compensation current source responsive to a voltage of the output power signal.

15. The wireless power enabled apparatus of claim 13 , further comprising control logic configured to enable the compensation current source during the communication period.

16. The wireless power enabled apparatus of claim 15 , wherein the control logic is further configured to:

sample a voltage level of the output power signal prior to the communication period; and

control the current through the compensation current source to maintain a voltage of the output power signal substantially near the sampled voltage.

17. The wireless power enabled apparatus of claim 15 , wherein the control logic is further configured to control the current through the compensation current source to maintain a voltage of the output power signal substantially near a predetermined voltage.

18. The wireless power enabled apparatus of claim 17 , further comprising:

a power management device configured to control supply of power for the wireless power enabled apparatus from the output power signal, a battery, or a combination thereof; and

wherein the control logic is further configured to control the current through the compensation current source to maintain a voltage of the output power signal to a level that triggers the power management device to supply the power for the wireless power enabled apparatus only from the battery.

19. The wireless power enabled apparatus of claim 13 , further comprising a variable load operably coupled to the output power signal wherein the compensation current source maintains the substantially constant voltage on the output power signal during fluctuations in the variable load occurring during the communication period.

20. The wireless power enabled apparatus of claim 19 , wherein the variable load includes at least one of a battery of the electronic device and system components of the electronic device.