Digital pre-distortion technique using nonlinear filters

Abstract

A linearizer and method. In a most general embodiment, the inventive linearizer includes a characterizer coupled to an input to and an output from said circuit for generating a set of coefficients and a predistortion engine responsive to said coefficients for predistorting a signal input to said circuit such that said circuit generates a linearized output in response thereto. In a specific application, the circuit is a power amplifier into which a series of pulses are sent during an linearizer initialization mode of operation. In a specific implementation, the characterizer analyzes finite impulse responses of the amplifier in response to the initialization pulses and calculates the coefficients for the feedback compensation filter in response thereto. In the preferred embodiment, the impulse responses are averaged with respect to a threshold to provide combined responses. In the illustrative embodiment, the combined responses are Fast Fourier Transformed, reciprocated and then inverse transformed. The data during normal operation is fed back to the data capture, corrected for distortion in the feedback path from the output of the amplifier, converted to basedband, synchronized and used to provide the coefficients for the predistortion linearization engine. As a result, in the best mode, each of the coefficients used in the predistortion linearization engine can be computed by solving the matrix equation HW=S for W, where W is a vector of the weights, S is a vector of predistortion linearization engine outputs, and H is a matrix of PA return path inputs as taught herein.