US 5,760,646 A · Feed-forward correction loop with adaptive predistortion injection for linearization of RF power amplifier

Abstract

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.

Claims19

Dependent claims

A method for correcting for distortion in an RF power amplifier comprising the steps of:

(a) monitoring an input signal supplied to and an amplified output signal from by said RF power amplifier, and extracting therefrom a distortion signal that varies with a rate of variation of the envelope of said amplified output signal;
(b) monitoring the instantaneous amplitude of said input signal to said amplifier, and generating at least one work function that varies with a variation of the instantaneous amplitude of said input signal;
c) generating a predistortion function in accordance with said distortion signal extracted in step (a) and said at least one work function of the instantaneous amplitude of said input signal as generated in step (b), so that said predistortion function varies with a rate of variation of the envelope of said amplified output signal;
(d) adaptively predistorting said input signal to be amplified by said RF amplifier at a rate of variation of the envelope of said amplified output signal, by predistorting said input signal by said predistortion function generated in step (c);
and (e) subjecting said amplified output signal from said RF power amplifier to a feed-forward correction loop.

2 more elements

A signal processing system for correcting for distortion in an RF power amplifier comprising:

a work function generator coupled to receive an input signal to be amplified by said RF power amplifier and being operative to generate at least one work function that varies with a variation of the instantaneous amplitude of said input signal;
a distortion signal extraction unit which is coupled to monitor said input signal and an amplified output signal from by said RF power amplifier, and to extract therefrom a distortion signal that varies with a rate of variation of the envelope of said amplified output signal;
a predistortion function generator, coupled to said work function generator and to said distortion signal extraction unit, and being operative to generate a predistortion function in accordance with said distortion signal and said at least one work function of the instantaneous amplitude of said input signal, so that said predistortion function varies with a rate of variation of the envelope of said amplified output signal;
a predistortion modulator coupled in the path of an input signal to be amplified by said RF power amplifier, and being operative to adaptively predistort said input signal at a rate of variation of the envelope of said amplified output signal, by predistorting said input signal by said predistortion control function;
and
a feed-forward correction loop connected in circuit with an output of said RF power amplifier.

3 more elements

Dependencies are inferred from the claim text.

Feed-forward correction loop with adaptive predistortion injection for linearization of RF power amplifier

Life of this patent

Feed-forward correction loop with adaptive predistortion injection for linearization of RF power amplifier

Life of this patent

Abstract

Claims19