An FIR Memory Polynomial Predistorter for Wideband RF Power Amplifiers

A memory polynomial (MP) based digital baseband predistorter for wideband base station RF power amplifiers is presented. The conventional memory polynomial based predistorter's inability to sufficiently improve the adjacent channel leakage ratio (ACLR) for high bandwidth signals is mitigated by using a linear FIR filter. The FIR filter compensates for the linear memory distortions and is employed prior to the memory polynomial predistorter (FIR-MP). The proposed technique is validated in simulations for 20 MHz and 80 MHz signals centered at 2 GHz. The PA models for the simulation are extracted from measurements carried out on a commercial 1W GaAs HBT PA. With considerably less number of coefficients, an ACLR improvement of at least 5.2 dB and 11.1 dB over the conventional MP DPD is obtained for 20 MHz and 80 MHz signals, respectively, and hence showing suitability for the adoption into small-cell base stations.