Power amplifier and method of operating a power amplifier

1. A power amplifier comprising:

a pulse wave modulation (PWM) controller;

a first power control stage configured to drive a first output between VDD and VSS in response to a control signal from the PWM controller;

a second power control stage configured to drive a second output between VDD and VSS in response to a control signal from the PWM controller; and a mid-voltage control circuit comprising:

a first switch connected to the first output to hold the voltage of the first output at a mid-voltage that is between VDD and VSS during an interval between when the first output is driven between VDD and VSS;

a second switch connected to the second output to hold the voltage of the second output at the mid-voltage during an interval between when the second output is driven between VDD and VSS; and

a voltage holding circuit connected between the first and second switches of the mid-voltage control circuit.

2. The power amplifier of claim 1 , wherein the voltage holding circuit includes an operational amplifier with one input connected between two series connected resistors, which are connected between VDD and VSS.

3. The power amplifier of claim 1 , wherein:

the first power control stage includes a high-side switch and a low-side switch in series and wherein the first output is connected between the high-side switch and the low-side switch;

the second power control stage includes a high-side switch and a low-side switch in series and wherein the second output is connected between the high-side switch and the low-side switch;

wherein the mid-voltage control circuit includes:

a first switch connected to the first output to hold the voltage of the first output at a mid-voltage that is between VDD and VSS during an interval between when the first output is driven between VDD and VSS; and

a second switch connected to the second output to hold the voltage of the second output at the mid-voltage during an interval between when the second output is driven between VDD and VSS.

4. The power amplifier of claim 3 , wherein the mid-voltage control circuit further includes a voltage holding circuit connected between the first and second switches of the mid-voltage control circuit.

5. The power amplifier of claim 4 wherein the voltage holding circuit includes an operational amplifier with one input connected between two series connected resistors, which are connected between VDD and VSS.

6. The power amplifier of claim 1 , wherein:

the first power control stage includes a high-side switch and a low-side switch in series and wherein the first output is connected between the high-side switch and the low-side switch;

the second power control stage includes a high-side switch and a low-side switch in series and wherein the second output is connected between the high-side switch and the low-side switch;

wherein the mid-voltage control circuit including:

a first switch connected to the first output to hold the voltage of the first output at a mid-voltage that is between VDD and VSS during an interval between when the first output is driven between VDD and VSS; and

a second switch connected to the second output to hold the voltage of the second output at the mid-voltage during an interval between when the second output is driven between VDD and VSS;

wherein the PWM controller is configured to:

provide a high-side switch control signal, P 1 , to control the high-side switch of the first power control stage and a low-side switch control signal, N 1 , to control the low-side switch of the first power control stage;

provide a high-side switch control signal, P 2 , to control the high-side switch of the second power control stage and a low-side switch control signal, N 2 , to control the low-side switch of the first power control stage; and

provide a freewheel control signal, FW, to control the first switch and the second switch of the mid-voltage control circuit.

7. The power amplifier of claim 6 , wherein the control signals P 1 , N 1 , P 2 , N 2 , and FW are digital signals.

8. The power amplifier of claim 1 , wherein the PWM controller is configured to provide control signals to the first power control stage, to the second power control stage, and to the mid-voltage control circuit to suppress 3 rd and 5 th harmonics.

9. A method for operating a power amplifier, the method comprising:

driving a first output between VDD and VSS;

driving a second output between VDD and VSS;

turning on a first switch of a mid-voltage control circuit to connect the first output to a voltage holding circuit to hold a voltage of the first output at a mid-voltage that is between VDD and VSS during an interval between when the first output is driven between VDD and VSS; and

turning on a second switch of the mid-voltage control circuit to connect to the second output to a voltage holding circuit to hold a voltage of the second output at the mid-voltage during an interval between when the second output is driven between VDD and VSS.

10. The method of claim 9 , further comprising:

controlling the interval during which the first switch is turned on to control the interval during which the voltage of the first output is held at the mid-voltage; and

controlling the interval during which the second switch is turned on to control the interval during which the voltage of the second output is held at the mid-voltage.

11. The method of claim 9 , further comprising controlling the interval during which the voltage of the first output is held at the mid-voltage and controlling the interval during which the voltage of the second output is held at the mid-voltage.