Predistortion system and method using analog feedback loop for look-up table training

• US 5,959,499 A
• Filed: 09/30/1997
• Issued: 09/28/1999
• Est. Priority Date: 09/30/1997
• Status: Expired due to Term

• Current Assignee: Motorola Solutions, Inc.
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Khan, Andrew Merritt, Opas, George Francis
• Primary Examiner(s): MOTTOLA, STEVEN J
• Application Number:
  US08/940,492
• Time in Patent Office: 728 Days
• Field of Search: 330/2, 330/129, 330/149, 455/115, 455/126
• US Class Current: 330/149
• CPC Class Codes: H03D 7/168 using a feedback loop containing mixers or demodulators
• CPC Class Codes: H03F 1/3247 using feedback acting on predistortion circuits H03F1/3264 takes precedence
• CPC Class Codes: H03F 1/345 using hybrid or directional couplers
• CPC Class Codes: H03F 2201/3233 Adaptive predistortion using lookup table, e.g. memory, RAM, ROM, LUT, to generate the predistortion

Abstract

The present invention provides a linearization system (100) and method (700, 800) for generating a predistorted drive signal for a nonlinear transmission path. The linearization includes: A) an analog feedback system (39), coupled to a computation unit, for determining, during a training mode, a complex error signal that linearizes the nonlinear transmission path and wherein, in an operation mode, the analog feedback system is disabled; and B) a computation unit (1), coupled to the analog feedback system and coupled to receive a complex input signal and the complex error signal, for determining, during the training mode, complex predistortion gain coefficients and, during the operation mode, generating the predistorted drive signal for the nonlinear transmission path, wherein the analog feedback system and computation unit are interconnected by interface circuitry.

Claims

1. A linearization system for providing a predistorted drive signal for a nonlinear transmission path, comprising:

A) an analog feedback system, coupled to a computation unit, for determining, during a training mode, a complex error signal that linearizes the nonlinear transmission path and wherein, in an operation mode, the analog feedback system is disabled; and

B) a computation unit, coupled to the analog feedback system and coupled to receive a complex input signal and the complex error signal, for determining, during the training mode, complex predistortion gain coefficients and, during the operation mode, generating the predistorted drive signal for the nonlinear transmission path,

wherein the analog feedback system and computation unit are interconnected by interface circuitry,

wherein the computation unit includes;

C) a ratio determiner, coupled to the interface circuitry and to receive the complex input signal, for determining a complex look-up table coefficient corresponding to a preselected signal level;

D) a lookup encoder, coupled to receive the complex input signal, for determining a magnitude of the complex input signal and generating an index based on the magnitude of the complex input signal and a preselected set of levels;

E) a look-up table, coupled to the ratio determiner and the lookup encoder, for outputting the complex look-up table coefficient corresponding to the index; and

F) a multiplier, coupled to receive the complex input signal and the complex look-up table coefficient, for multiplying the complex input signal and the complex look-up table coefficient to provide the predistorted drive signal.

2. The linearization system of claim 1 wherein the preselected set of levels is based on steps of the input signal magnitude.

3. A method for generating a predistorted drive signal for a nonlinear transmission path that includes a power amplifier, comprising the steps of:

A) utilizing an analog feedback system to determine a complex error signal that linearizes the nonlinear transmission path; and

B) determining a magnitude of a complex input signal and generating a predistorted drive signal for the nonlinear transmission path that includes the power amplifier,

wherein determining a magnitude of the complex input signal and generating a predistorted drive signal for the nonlinear transmission path includes;

C) converting the complex error signal to baseband digital format;

D) determining a complex gain coefficient corresponding to a preselected power level and storing the complex gain coefficient in a look-up table;

E) determining a magnitude of the complex input signal and generating an index based on the magnitude of the complex input signal and the preselected power level;

F) using the look-up table to output the complex gain coefficient corresponding to the index; and

G) multiplying the complex input signal and the complex gain coefficient to provide the predistorted drive signal.

4. The method of claim 3 wherein a preselected set of power levels is based on steps of the input signal magnitude.

5. A radio having a linearization system for providing a predistorted drive signal for a nonlinear transmission path that includes a power amplifier, the linearization system comprising:

A) an analog feedback system that includes the nonlinear transmission path, coupled to the computation unit, for determining the complex error signal that linearizes the nonlinear transmission path; and

B) a computation unit, coupled to the analog feedback system and coupled to receive a complex input signal and a complex error signal, for determining a magnitude of the complex input signal and generating the predistorted drive signal for the nonlinear transmission path that includes the power amplifier,

wherein the computation unit includes;

C) a ratio determiner, coupled to the interface circuitry and to receive the complex input signal, for determining a complex look-up table coefficient corresponding to a preselected signal level;

D) a lookup encoder, coupled to receive the complex input signal, for determining a magnitude of the complex input signal and generating an index based on the magnitude of the complex input signal and a preselected set of levels;

E) a look-up table, coupled to the ratio determiner and the lookup encoder, for outputting the complex look-up table coefficient corresponding to the index; and

F) a multiplier, coupled to receive the complex input signal and the complex look-up table coefficient, for multiplying the complex input signal and the complex look-up table coefficient to provide the predistorted drive signal.