Process for compensating nonlinearities in an amplifier circuit

• US 5,164,678 A
• Filed: 07/11/1991
• Issued: 11/17/1992
• Est. Priority Date: 07/12/1990
• Status: Expired due to Term

• Current Assignee: Thomcast AG
• Original Assignee: ASEA Brown Boveri SA de CV (ABB Limited)
• Inventors: Puri, Narindra N., Boksberger, Hans Ulrich
• Primary Examiner(s): Laroche, Eugene R.
• Assistant Examiner(s): DINH, TAN X
• Application Number:
  US07/728,733
• Time in Patent Office: 495 Days
• Field of Search: 330/149, 330/151, 328/163, 455/50, 455/63, 455/295
• US Class Current: 330/149
• CPC Class Codes: H03F 1/3247 using feedback acting on predistortion circuits H03F1/3264 takes precedence
• CPC Class Codes: H03F 1/3252 using multiple parallel paths between input and output H03F1/3258, H03F1/3282, H03F1/3294 take precedence
• CPC Class Codes: H03F 2201/3231 Adaptive predistortion using phase feedback from the output of the main amplifier

Abstract

A process for compensating nonlinearities in an amplifier circuit. An input signal s(t) is amplified to form an output signal y(t) using an amplifier circuit subject to nonlinearities. In accordance with the invention, a predistortion filter is connected upstream of the amplifier circuit. An aggregate signal ##EQU1## is formed in said filter from the input signal s(t) and a predistorted signal x(t) fed back from the output of the predistortion filter, and integrated with respect to time. The predistorted signal x(t) is fed to the amplifier circuit subject to nonlinearities. In this case, the prescribed number n+1 of coefficients k₀, . . . , K_n is determined in accordance with the model ##EQU2## so that for a given input signal x(t) of the amplifier circuit the output signal determined in accordance with the model is essentially identical with the output signal y(t) of the amplifier circuit.

Claims

1. A process for compensating nonlinearities in an amplifier circuit, in which an input audio signal s(t) is amplified to form an output audio signal y(t) using a prescribed amplifier circuit subject to nonlinearities, comprising:

determining a prescribed number n+1 of coefficients k₀, . . . , k_n of the amplifier circuit in accordance with the model ##EQU26## so that for a given input signal x(t) of the amplifier circuit the output signal determined in accordance with the model is essentially identical with the actual output signal y(t) of the amplifier circuit,

producing an aggregate signal ##EQU27## in a predistortion filter from the input signal s(t), integrating the aggregate signal with respect to time in an integrator to form a predistorted signal x(t), and

feeding back a predistorted signal x(t) fed back to the predistortion filter, and

feeding a predistorted signal from the output of the predistortion filter x(t) to the amplifier circuit subject to nonlinearities.

3. The process as claimed in claim 1 or 2, wherein for the purpose of determining the prescribed number n+1 of coefficients k₀, . . . , k_n

determining an estimated signal ##EQU30## in an identification processor from the immediate input signal x(t) of the nonlinear amplifier circuit in accordance with the model of the amplifier circuit,

forming an error signal e(t) from the difference between this estimated signal u(t) and the actual output signal y(t) of the amplifier circuit, and

forming the coefficients k₀, . . . , k_n are formed from the said input signal x(t) and the error signal e(t) in accordance with the following rules:

##EQU31##

4. The process as claimed in claim 1 or 2, wherein the coefficients k=[k₀, k₁, . . . , k_n ]^T are determined in an identification processor from the immediate input signal x(t) of the nonlinear amplifier circuit and the actual output signal y(t) of the amplifier circuit in accordance with

5. The process as claimed in claim 1 or 2, wherein

the immediate input signal x(t) of the nonlinear amplifier circuit and the output signal y(t) are each submitted to a fast Fourier transformation, and

the coefficients k=[k₀, k₁, . . . , k_n ]^T are determined in an identification processor from the Fourier-transformed signals in accordance with

7. The process as claimed in claim 4, wherein the components of the vectors r(j), k(j) and of the matrices G(j) are updated in accordance with

8. The process as claimed in claim 1 or 2, wherein the predistortion filter operates with n+1=4 coefficients k₀, . . . , k₃.

9. The process as claimed in claim 1, wherein the coefficients k₀, . . . , k_n are continuously redetermined, resulting in adaptive compensation of the nonlinearities.

2. A process for compensating nonlinearities in an amplifier circuit, in which an input audio signal s(t) is amplified to form an output audio signal y(t) using an amplifier circuit subject to nonlinearities, comprising:

determining a prescribed number n+1 of coefficients k₀, . . . , k_n of the amplifier circuit in accordance with the model ##EQU28## so that for a given input signal x(t) of the amplifier circuit the output signal determined in accordance with the model is essentially identical with the actual output signal y(t) of the amplifier circuit,

obtaining a compensation signal c(j) in a predistortion filter from the digitized input signal s(j) in accordance with ##EQU29## adding the compensation signal to the input signal, and feeding the resulting signal x(t) to the amplifier circuit subject to nonlinearities.

6. The process as claimed in claim 2, wherein by contrast with claim 2 the compensation signal c(j) is determined from the digitized input signal s(j) in accordance with ##EQU32##

10. An arrangement for the linear amplification of signals, in particular for the power amplification of audio signals, comprising an amplifier circuit subject to nonlinearities for generating signals of high power, wherein

first means are provided in order for determining a prescribed number n+1 of coefficients k₀, . . . , k_n of the amplifier circuit in accordance with the model ##EQU33## so that for a given input signal x(t) of the amplifier circuit the output signal determined in accordance with the model is essentially identical with the output signal y(t) of the amplifier circuit,

a predistortion filter is provided before the amplifier circuit, in which filter an aggregate signal ##EQU34## is formed from the input signal s(t) of the arrangement and a predistorted signal x(t) fed back from the output of the predistortion filter,

an integrator is provided for integrating with respect to time the aggregate signal to form a predistorted signal x(t), and

the signal x(t) predistorted by the predistortion filter is fed to the amplifier circuit subject to nonlinearities.