Class D power amplifier

1. An apparatus comprising:

a driver having an input, an output, and a parasitic capacitance, wherein the input of the driver is configured to receive complementary first and second radio frequency (RF) signals, and wherein there is a free-fly interval between consecutive pulses from the first and second RF signals, and wherein the parasitic capacitance of the driver creates switching losses;

an output capacitor that is coupled to the output of the driver;

a matching network that is coupled to the output capacitor; and

a cancellation circuit that is coupled to the output of the driver so as to provide harmonic restoration at least during the free-fly interval.

2. The apparatus of claim 1 , wherein the cancellation circuit is an active circuit.

3. The apparatus of claim 1 , wherein the cancellation circuit is a passive circuit.

4. The apparatus of claim 3 , wherein the cancellation circuit is a tunable inductor-capacitor (LC) circuit.

5. The apparatus of claim 4 , wherein the driver further comprises:

a first transistor having a first passive electrode, a second passive electrode, and a control electrode, wherein the first transistor is configured to receive the first RF signal at its control electrode, and wherein the second passive electrode of the first transistor is coupled to the output of the driver; and

a second transistor having a first passive electrode, a second passive electrode, and a control electrode, wherein the second transistor is configured to receive the second RF signal at its control electrode, and wherein the first passive electrode of the first transistor is coupled to the output of the driver.

6. The apparatus of claim 5 , wherein the tunable LC circuit further comprises an adjustable capacitor and an inductor coupled in series with one another.

7. The apparatus of claim 6 , wherein the first and second transistors further comprise a PMOS transistor and an NMOS transistor, respectively.

8. The apparatus of claim 7 , wherein the PMOS transistor further comprises a plurality of PMOS transistors coupled in parallel with one another.

9. An apparatus comprising:

a first driver having an input, an output, and a parasitic capacitance, wherein the input of the first driver is configured to receive complementary first and second RF signals, and wherein there is a free-fly interval between consecutive pulses from the first and second RF signals;

a second driver having an input, an output, and a parasitic capacitance, wherein the input of the second driver is configured to receive the first and second RF signals;

an first output capacitor that is coupled to the output of the first driver;

a second output capacitor that is coupled to the output of the second driver;

a matching network that is coupled to each of the first and second output capacitors; and

a cancellation circuit that is coupled to the output of at least one of the first and second drivers so as to provide harmonic restoration at least during the free-fly interval.

10. The apparatus of claim 9 , wherein the cancellation circuit is a passive circuit.

11. The apparatus of claim 10 , wherein the cancellation circuit is a tunable LC circuit.

12. The apparatus of claim 11 , wherein the first and second drivers each further comprises:

a first transistor having a first passive electrode, a second passive electrode, and a control electrode, wherein the first transistor is configured to receive the first RF signal at its control electrode, and wherein the second passive electrode of the first transistor is coupled to the output of it driver; and

a second transistor having a first passive electrode, a second passive electrode, and a control electrode, wherein the second transistor is configured to receive the second RF signal at its control electrode, and wherein the first passive electrode of the first transistor is coupled to the output of it driver.

13. The apparatus of claim 12 , wherein the tunable LC circuit further comprises an adjustable capacitor and an inductor coupled in series with one another.

14. The apparatus of claim 13 , wherein the first and second transistors further comprise a PMOS transistor and an NMOS transistor, respectively.

15. The apparatus of claim 14 , wherein the PMOS transistor further comprises a plurality of PMOS transistors coupled in parallel with one another.

16. The apparatus of claim 14 , wherein the apparatus further comprises:

a first switch network that is coupled to the input of the first driver; and

a second switch network that is coupled to the input of the second driver.

17. The apparatus of claim 16 , wherein the apparatus further comprises:

a first switch that is coupled between the cancellation circuit and the output of the first driver; and

a second switch that is coupled between the cancellation circuit and the output of the second driver.

18. The apparatus of claim 17 , wherein the first and second switches each further comprise an NMOS transistor with a floating body and gate.

19. The apparatus of claim 16 , wherein the cancellation circuit further comprises:

a first cancellation circuit that is coupled to the output of the first driver; and

a second cancellation circuit that is coupled to the output of the second driver.

20. An apparatus comprising:

a plurality of drivers, wherein each driver has an input, an output, and a parasitic capacitance, wherein the input of the each driver is configured to receive complementary first and second RF signals, and wherein there is a free-fly interval between consecutive pulses from the first and second RF signals;

a plurality of output capacitor, wherein each output capacitor is coupled to the output of at least one of the drivers;

a matching network that is coupled to each of the output capacitors; and

a cancellation circuit that is coupled to the output of at least one of the drivers so as to provide harmonic restoration at least during the free-fly interval.

21. The apparatus of claim 20 , wherein the cancellation circuit is a passive circuit.

22. The apparatus of claim 21 , wherein the cancellation circuit is a tunable LC circuit.

23. The apparatus of claim 22 , wherein each driver further comprises:

a first transistor having a first passive electrode, a second passive electrode, and a control electrode, wherein the first transistor is configured to receive the first RF signal at its control electrode, and wherein the second passive electrode of the first transistor is coupled to the output of it driver; and

a second transistor having a first passive electrode, a second passive electrode, and a control electrode, wherein the second transistor is configured to receive the second RF signal at its control electrode, and wherein the first passive electrode of the first transistor is coupled to the output of it driver.

24. The apparatus of claim 23 , wherein the tunable LC circuit further comprises an adjustable capacitor and an inductor coupled in series with one another.

25. The apparatus of claim 24 , wherein the first and second transistors further comprise a PMOS transistor and an NMOS transistor, respectively.

26. The apparatus of claim 24 , wherein the PMOS transistor further comprises a plurality of PMOS transistors coupled in parallel with one another.

27. The apparatus of claim 24 , wherein the apparatus further comprises a plurality of switch networks, wherein each switch network is coupled to the input of at least one of the drivers.

28. The apparatus of claim 27 , wherein the apparatus further comprises a plurality of switches, wherein each switch is coupled between the cancellation circuit and the output of at least one of the drivers.

29. The apparatus of claim 28 , wherein each switch further comprises an NMOS transistor with a floating body and gate.

30. The apparatus of claim 27 , wherein the cancellation circuit further comprises a plurality of cancellation circuits, wherein each cancellation circuit is coupled to the output of at least one of the drivers.