Patent ID: 7805115

Claim:
A radio frequency output power control system for use in communication systems that use a modulation scheme having a non-constant amplitude envelope, the system comprising: a power amplifier comprising a radio frequency input node for receiving a radio frequency input signal, a power control node for receiving a power control signal, and an output for providing an amplified output signal; an envelope detection unit that receives the radio frequency input signal and provides a positive current output and a negative current output in accordance therewith; a differential variable filter that converts the positive current output to a positive voltage output, converts the negative current output to a negative voltage output, filters the positive and negative voltage outputs, and provides a filtered power signal while allowing the envelope of the power signal to pass; and a comparison unit that compares the filtered power signal to a power level of the amplified output signal and provides the error signal to the power control node of the power amplifier to cancel amplitude modulation from the amplified output signal, wherein the variable filter has a first time constant for providing a fast transient response to changes in a power level of the input signal and a second time constant for filtering the input signal.