Spectrian Corporation

Kent E Bagwell

Donald K Belcher

Michael Andrew Wohl

The envelope-dependency of the distortion-introducing behavior of an RF power amplifier is used to derive a predistortion signal, that is derived from a plurality of respectively different work function representative signals. Each work function signal, in turn, is based upon the envelope of the input signal to the RF power amplifier. Prior to being combined into a predistortion control signal, each work function signal is controllably weighted in accordance with an error measurement comparison of the amplifier input signal with the amplifier output signal. The error measurement function yields a measure of the error contained in the amplifier output signal, and drives a weight adjustment control mechanism, which controllably varies a set of weights for each of in-phase and quadrature components of the respectively different signal functions, in such a manner as to minimize the measured error.

Adaptive compensation of RF amplifier distortion by injecting

The envelope-dependency of the distortion-introducing behavior of an RF power amplifier is used to derive a predistortion signal, that is derived from a plurality of respectively different work function representative signals. Each work function signal, in turn, is based upon the envelope of the input signal to the RF power amplifier. Prior to being combined into a predistortion control signal, each work function signal is controllably weighted in accordance with an error measurement comparison of the amplifier input signal with the amplifier output signal. The error measurement function yields a measure of the error contained in the-amplifier output signal, and drives a weight adjustment control mechanism, which controllably varies a set of weights for each of in-phase and quadrature components of the respectively different signal functions, in such a manner as to minimize the measured error.

A linearization scheme for an RF power amplifier combines an adaptive predistortion modulator with a feedforward error correction loop, which cancels noise imparted by predistortion modulation to the amplified signal, and minimizes distortion in the RF amplifier's output to a level that allows the use of a low cost auxiliary RF error amplifier in the feed-forward loop. The predistortion correction mechanism produces a predistortion signal based upon the input signal and is adaptively adjusted by an error signal extracted from the output of the a main RF power amplifier. The input signal is supplied to a work function generator unit and to a subtraction unit, which is also coupled to receive a fractional portion of the amplifier output signal and outputs the RF error component. The RF error component is coupled to a predistortion function generator, which is driven by the work function generator unit. The predistortion modulator uses the output of the predistortion function generator to predistort the input signal by a compensation characteristic equal and opposite to the distortion expected at the output of the main RF amplifier. When subjected to the transfer function of the RF amplifier, the predistortion signal injected into the input signal path will effectively cancel the amplifier's anticipated distortion behavior. The predistortion is made adaptive by tracking the error signal and coupling this error signal to the predistortion function generator.

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Rogersville, TN, United States of America

Kent E Bagwell