Large signal polar modulated power amplifier
View Patent ↗Polar modulation input signals to a polar modulated power amplifier include a phase modulated (PM) input signal, which feeds a power amplifier input, and an amplitude modulated (AM) input signal, which provides an envelope supply voltage for the power amplifier. The present invention is a large signal polar modulated power amplifier that extends the effective amplitude range of AM input signals that can be handled by the power amplifier by amplitude modulating the PM input signal using the AM input signal. Amplitude modulating the PM input signal effectively lowers the amplitude of the PM input signal when the amplitude of the AM input signal is lowered, which maintains adequate headroom between the power amplifier's signal input and envelope supply voltage input in the presence of large amplitude AM input signals. As a result, the power amplifier can amplify larger amplitude AM input signals than traditional power amplifier designs.
1. A polar modulated power amplifier circuit comprising:
an amplitude modulation circuit adapted to:
receive a phase modulated (PM) input signal;
receive a first amplitude modulated (AM) input signal;
provide a PM final stage signal, wherein an amplitude of the PM final stage signal is based on the first AM input signal, and a phase of the PM final stage signal is based on the PM input signal; and
control the amplitude of the PM final stage signal to prevent a base-to-collector junction of a base and a collector from becoming forward biased; and
a final amplifier stage:
comprising:
the base adapted to receive the PM final stage signal; and
the collector adapted to receive a second AM input signal; and
adapted to provide a polar modulated output signal, wherein an amplitude of the polar modulated output signal is based on the second AM input signal, and a phase of the polar modulated output signal is based on the PM final stage signal.
2. The power amplifier circuit of claim 1 wherein the amplitude of the PM final stage signal is based on an amplitude of the first AM input signal.
3. The power amplifier circuit of claim 2 wherein the amplitude of the PM final stage signal decreases as the amplitude of the first AM input signal decreases.
4. The power amplifier circuit of claim 1 wherein the phase of the PM final stage signal is based on a phase of the PM input signal.
5. The power amplifier circuit of claim 1 wherein the amplitude of the polar modulated output signal is based on an amplitude of the second AM input signal.
6. The power amplifier circuit of claim 1 wherein the phase of the polar modulated output signal is based on the phase of the PM final stage signal.
7. The power amplifier circuit of claim 1 wherein the first AM input signal is substantially identical to the second AM input signal.
8. The power amplifier circuit of claim 1 wherein the second AM input signal is substantially proportional to the first AM input signal.
9. The power amplifier circuit of claim 1 wherein the second AM input signal is substantially proportional to the first AM input signal plus an offset.
10. The power amplifier circuit of claim 1 wherein the final amplifier stage further comprises an array of one or more bipolar NPN transistors having the base and the collector.
11. The power amplifier circuit of claim 1 wherein the amplitude modulation circuit further comprises:
a PM input adapted to receive the PM input signal;
a PM output adapted to provide the PM final stage signal; and
a variable impedance element,
wherein the PM input is coupled to the PM output, and the variable impedance element is coupled between the PM output and ground.
12. The power amplifier circuit of claim 11 wherein the amplitude of the PM final stage signal is controlled by varying an impedance of the variable impedance element.
13. The power amplifier circuit of claim 12 wherein the amplitude of the PM final stage signal decreases as the impedance of the variable impedance element decreases.
14. The power amplifier circuit of claim 12 wherein the variable impedance element further comprises a diode element.
15. The power amplifier circuit of claim 12 wherein the impedance of the variable impedance element is controlled by varying a control current flowing through the variable impedance element.
16. The power amplifier circuit of claim 12 wherein the impedance of the variable impedance element increases as an amplitude of the first AM input signal increases.
17. The power amplifier circuit of claim 1 wherein the first AM input signal is provided from an amplitude modulated power supply output.
18. The power amplifier circuit of claim 1 wherein the first AM input signal is provided from an amplitude modulated power supply input.