A DSP controlled adaptive feedforward amplifier linearizer

Abstract

Currently, the only available wideband (multiple MHz) amplifier linearization method is feedforward. Feedforward, though, requires automatic adaptation of key parameters for reliable distortion cancellation as operating conditions vary. With a novel and appropriate use of DSP, we have implemented a feedforward linearizer with adaptation driven by easily computed gradient signals. This overcomes the difficulties, such as DC offsets at the output of analog mixers and masking of weak signals by stronger ones, that slow and/or cause incorrect convergence of many previously reported implementations. The result is an average of 40 dB reduction in intermodulation spectra over a wide bandwidth, with extremely fast tracking.