Spectral distortion monitor for controlling pre-distortion and feed-forward linearization of rf power amplifier

Abstract

A carrier cancellation combiner, and pre-distortion and feed-forward loops of an RF power amplifier are controlled to minimize IMD components at the output of the RF amplifier, by a spectral distortion measurement scheme that performs Fast Fourier Transform (FFT)-based spectral power measurements at a 'reference' signal port (associated with the RF input signal), and a plurality of 'test' signal ports (associated with various monitoring locations of the amplifier). Signals extracted from the control and test ports are downconverted to baseband, bandpass filtered, digitized and stored as a spectral ‘snapshot’ of the entire band of the signal infrastructure of the amplifier. A digital signal processor-based controller processes the buffered data to produce averaged FFT's of the data extracted from the reference and test ports and thereby provide spectral information for each sampled signal set. The FFT for the control data is processed to establish a baseline, with which the FFTs for the test data are compared, to generate adjustment signals for control parameters through which IMD components introduced by the amplifier may be minimized.