Intermodulation compensation in multi-channel amplifiers

• US 6,233,436 B1
• Filed: 06/09/1999
• Issued: 05/15/2001
• Est. Priority Date: 12/16/1996
• Status: Expired due to Term

• Current Assignee: Unwired Planet LLC (JP Morgan Chase & Co)
• Original Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Inventors: Dent, Paul W.
• Primary Examiner(s): LE, THANH C
• Application Number:
  US09/328,903
• Time in Patent Office: 706 Days
• Field of Search: 455/12.1, 455/15, 455/17, 455/19, 455/25, 455/63, 455/91, 455/115, 455/101, 455/102, 455/103, 455/67.1, 455/226.1, 375/295, 375/296, 330/124.R, 330/151, 330/295
• US Class Current: 455/114.2
• CPC Class Codes: H03F 1/3223 using feed-forward H03F1/3211 takes precedence

Abstract

A multi-channel transmit amplifier array comprising a multiplicity N of coupled power amplifier elements is disclosed. The number of channels provided for amplifying desired signals for transmission is less than N, by at least one. In this case, the unused channel is used to inject an intermodulation compensation waveform specifically tailored to reduce intermodulation generated in all of the other N−1 signal paths. Instantaneous complex waveform values for the intermodulation compensation waveform may be systematically computed from the instantaneous complex values of the N−1 desired signals in such a way as to minimize the greatest signal amplitude in any of the N signal paths.

Claims

1. An apparatus for reducing intermodulation distortion during a radiotelephone communication, comprising:

a plurality of generators each comprising a voice coder for digitizing, compressing and error correction coding a voice signal, said voice coder also providing voice activity signal indicative of the presence or absence of speech;

modulation means for impressing the coded, digital voice signal on a radio frequency carrier for transmission;

a waveform generator for computing at least one intermodulation compensation waveforms that are a function of the active speech modulated signals; and

a switching means operated by said voice activity indicating signal for selecting either the speech modulated radio signal from said modulation means when speech is present and for selecting an intermodulation compensation waveform from said waveform generator during speech pauses.

2. A method for reducing intermodulation distortion during a radiotelephone communication, comprising the steps of:

digitizing, compressing and error correction coding a voice signal in a plurality of generators;

producing a voice activity signal indicative of the presence or absence of speech;

impressing the coded, digital voice signal on a radio frequency carrier for transmission;

computing at least one intermodulation compensation waveforms that are a function of the active speech modulated signals; and

selecting either the speech modulated radio signal from said modulation means when speech is present and for selecting an intermodulation compensation waveform from said waveform generator during speech pauses depending upon the voice activity indicating signal.