Adaptive supply voltage for a power amplifier
In one embodiment, a signal-processing apparatus for generating an amplified output signal based on an input signal is provided. The apparatus comprises: an amplifier configured to generate the output signal, wherein the amplifier is configured to receive a supply voltage; and a limiter configured to inhibit increases in the input signal power level from being applied to the amplifier, wherein the limiter comprises: a variable attenuator configured to selectively attenuate the input signal before being applied to the amplifier; wherein the limiter integrates over a voltage difference between a current measure of attenuated input signal power level and a limiter threshold level to control a level of attenuation applied by the variable attenuator to the input signal.
1. A signal-processing system for generating an amplified output signal based on an input signal, the system comprising:
an amplifier configured to generate the output signal, wherein the amplifier is configured to receive a supply voltage; and
a limiter configured to inhibit increases in the input signal power level from being applied to the amplifier, wherein the limiter comprises:
a variable attenuator configured to selectively attenuate the input signal before being applied to the amplifier;
wherein the limiter integrates over a voltage difference between a current measure of attenuated input signal power level and a limiter threshold level to control a level of attenuation applied by the variable attenuator to the input signal;
wherein a control unit is configured to drive the limiter threshold level as a function of the supply voltage.
2. The system of claim 1 , wherein the current measure of attenuated input signal power level is a function of a current root-mean-square (RMS) power level of an attenuated radio frequency (RF) signal applied to the amplifier.
3. The system of claim 1 , wherein the current measure of attenuated input signal power level is a function of an RF signal tapped from the input signal after attenuation of the input signal by the variable attenuator.
4. The system of claim 1 , wherein the limiter further comprises:
attenuator control circuitry configured to generate an attenuator control signal to control the level of attenuation applied by the variable attenuator to the input signal.
5. The system of claim 4 , wherein the attenuator control circuitry comprises an op amp configured to generate the attenuator control signal based on a difference between a current measure of attenuated input signal power level and a limiter threshold level.
6. The system of claim 4 , wherein the attenuation level of the variable attenuator is based on magnitude of the attenuator control signal when the attenuator control signal is positive.
7. The system of claim 1 , wherein the limiter further comprises attenuator control circuitry comprising a software-based control unit configured to execute software to drive the limiter threshold signal towards a measure of the input signal after attenuation of the input signal by the variable attenuator.