US 5,124,665 A · Circuit for reducing distortion produced by an r.f. power amplifier

Abstract

A high frequency SSB radio transmitter has an envelope amplitude modulator for varying the envelope of an r.f. signal source based on an error signal from envelope detectors detecting the envelope of the input and output waveform. It also has a phase modulator for varying the phase of the input waveform based on differences detected in a second amplitude modulator between the instantaneous phase of the input and output r.f. signal. A signal derived from the error signal controls the second amplitude modulator in a subsidiary feedback loop to maintain the size of the envelopes detected by the detectors the same, in order that a difference amplifier may operate effectively. Rapid discrepancies between the detected envelopes occurring within an envelope can then be corrected by the envelope amplitude modulator.

Claims13

Dependent claims

A circuit for reducing envelope amplitude distortion produced by an r.f. power amplifier, said r.f. power amplifier having an input and an output, for an r.f. signal source, comprising a main feedback loop for reducing envelope amplitude errors between the output of the power amplifier and the r.f. signal source, the main feedback loop including envelope detector means for generating an error signal, dependent on the envelope amplitude of a signal derived from the power amplifier output and received at a first input of said envelope detector means relative to that of a signal derived from the r.f. signal source and received at a second input of the envelope detector means, a signal derived from the error signal being used to modulate the envelope amplitude of the power amplifier input, and a subsidiary feedback loop by means of which a signal derived from the error signal is used to modulate the envelope amplitude of one input to the envelope detector means so as to tend to hold both inputs to the envelope detector means the same.

A circuit for reducing envelope amplitude distortion produced at an output of an r.f. power amplifier in response to a signal applied to an input thereof from an r.f. source, comprising

envelope detector means having a first input coupled to the output of said power amplifier and a second input coupled to said r.f. source, said envelope detector means generating an error signal at an output thereof which is dependent on the envelope amplitude of a signal received from said power amplifier at the first input thereof and on a signal received from said r.f. source at the second input thereof;
a first amplitude modulator interposed between said r.f. source and said power amplifier, said first amplitude modulator having a first input coupled to said r.f. source and an output coupled to the input of said power amplifier;
a second amplitude modulator interposed between the output of said power amplifier and the first input of said envelope detector means, said second amplitude modulator having a first input coupled to the output of said power amplifier and an output coupled to the first input of said envelope detector means;
and
means coupling the error signal at the output of said envelope detector means to second inputs of said first and second amplitude modulators thereby modulating the envelope amplitude of the signal at the input of said power amplifier and the signal at the first input of said envelope detector means, whereby the signals received at the first and second inputs of said envelope detector means tend to be the same.

2 more elements

Dependencies are inferred from the claim text.

Circuit for reducing distortion produced by an r.f. power amplifier

Life of this patent

Circuit for reducing distortion produced by an r.f. power amplifier

Life of this patent

Abstract

Claims13