Charging pads and methods for charging receiver devices having different frequency standards

1. A charging pad configured to wirelessly transfer electrical power to a plurality of receiver devices, wherein the charging pad comprises:

a power drive unit comprising:

a first oscillator configured to generate a first alternating current voltage signal having a first frequency;

a first amplifier coupled to the first oscillator and configured to amplify the first AC voltage signal having the first frequency;

a second oscillator configured to generate a second AC voltage signal having a second frequency;

a second amplifier coupled to the second oscillator and configured to amplify the second AC voltage signal having the second frequency; and

an adder configured to combine the amplified first AC voltage signal and the amplified second AC voltage signal to produce a combined voltage signal; and

a transmitting unit operatively coupled to the power drive unit and comprising:

at least one first frequency coil tuned to the first frequency and configured to receive at least a portion of the amplified first AC voltage signal from the combined voltage signal and transmit the amplified first AC voltage signal having the first frequency; and

at least one second frequency coil tuned to the second frequency and configured to receive at least a portion of the amplified second AC voltage signal from the combined voltage signal and transmit the amplified second AC voltage signal having the second frequency.

2. The charging pad of claim 1 , further comprising a first power unit operatively coupled to the first oscillator and the second oscillator and configured to supply a first bias voltage to the first oscillator and the second oscillator.

3. The charging pad of claim 1 , further comprising a second power unit operatively coupled to the first amplifier and the second amplifier and configured to supply a second bias voltage to the first amplifier and the second amplifier.

4. The charging pad of claim 1 , wherein the adder is configured to combine the amplified first AC voltage signal and the amplified second AC voltage signal to generate the combined voltage signal comprising the first frequency and the second frequency.

5. The charging pad of claim 4 , wherein the adder is further configured to transmit the combined voltage signal to the at least one first frequency coil and the at least one second frequency coil.

6. The charging pad of claim 5 , wherein the at least one first frequency coil is configured to receive the combined voltage signal and resonate at the first frequency to transmit the amplified first AC voltage signal having the first frequency to a first receiver coil of a first receiver device.

7. The charging pad of claim 6 , further comprising a first controller operatively coupled to the first receiver coil and the first amplifier, wherein the first controlleris configured to control a voltage gain of the first amplifier.

8. The charging pad of claim 5 , wherein the at least one second frequency coil is configured to receive the combined voltage signal and resonate at the second frequency to transmit the amplified second AC voltage signal having the second frequency to a second receiver coil of a second receiver device.

9. The charging pad of claim 8 , further comprising a second controller operatively coupled to the second receiver coil and the second amplifier, wherein the second controller is configured to control a voltage gain of the second amplifier.

10. A charging pad configured to wirelessly transfer electrical power to a plurality of receiver devices, wherein the charging pad comprises:

a power drive unit comprising:

an oscillator configured to generate a first AC voltage signal having a first frequency;

a bridge converter configured to convert a DC voltage signal into a second AC voltage signal having a second frequency;

an amplifier coupled to the oscillator and configured to amplify the first AC voltage signal having the first frequency; and

a transformer operatively coupled to the amplifier and the bridge converter and configured to combine the amplified first AC voltage signal and the second AC voltage signal; and

a transmitting unit operatively coupled to the power drive unit and comprising:

at least one first frequency coil tuned to the first frequency to transmit the amplified first AC voltage signal having the first frequency; and

at least one second frequency coil tuned to the second frequency to transmit the second AC voltage signal having the second frequency.

11. The charging pad of claim 10 , further comprising a first power unit operatively coupled to the oscillator and configured to supply a bias voltage to the oscillator to generate the first AC voltage signal.

12. The charging pad of claim 10 , further comprising a second power unit operatively coupled to the bridge converter and configured to supply an input power having the DC voltage signal to the bridge converter.

13. The charging pad of claim 12 , wherein the second power unit is operatively coupled to the amplifier and configured to supply the second bias voltage signal to the amplifier to amplify the first AC voltage signal.

14. The charging pad of claim 10 , wherein the transformer comprises:

a first winding coupled to the oscillator and configured to receive the amplified first AC voltage signal; and

a second winding coupled to the bridge converter and configured to receive the second AC voltage signal.

15. The charging pad of claim 14 , wherein the transformer is configured to combine the amplified first AC voltage signal and the second AC voltage signal to generate a combined voltage signal having the first frequency and the second frequency, wherein the combined voltage signal is received by the at least one first frequency coil and the at least one second frequency coil.

16. The charging pad of claim 15 , wherein the at least one first frequency coil is configured to receive the combined voltage signal and resonate at the first frequency to transmit the amplified first AC voltage signal having the first frequency to a first receiver device of the plurality of receiver devices.

17. The charging pad of claim 16 , further comprising a second controller operatively coupled to the first receiver device and the bridge converter, wherein the second controller is configured to vary a switching frequency or a duty ratio of switching signals transmitted to the bridge converter to regulate the second AC voltage signal.

18. The charging pad of claim 15 , wherein the at least one second frequency coil is configured to receive the combined voltage signal and resonate at the second frequency to transmit the received second AC voltage signal having the second frequency to a second receiver device of the plurality of receiver devices.

19. The charging pad of claim 18 , further comprising a first controller operatively coupled to the second receiver device and the amplifier, wherein the first controller is configured to control a voltage gain of the amplifier.

20. A charging pad, comprising:

a power drive unit comprising:

a first oscillator configured to generate a first AC voltage signal having a first frequency;

a second oscillator configured to generate a second AC voltage signal having a second frequency;

an adder operatively coupled to the first oscillator and the second oscillator, wherein the adder is configured to:

combine the first AC voltage signal and the second AC voltage signal to produce a combined voltage signal; and

amplify the combined voltage signal having the first frequency and the second frequency; and

a transmitting unit operatively coupled to the power drive unit and comprising:

at least one first frequency coil tuned to the first frequency and configured to receive the amplified combined voltage signal and transmit the first AC voltage signal having the first frequency; and

at least one second frequency coil tuned to the second frequency and configured to receive the amplified combined voltage signal and transmit the second AC voltage signal having the second frequency.