A Wideband Mixed-Signal Predistorter for Small-Cell Base Station Power Amplifiers

Abstract

A novel low-power wideband mixed-signal approach to linearize RF power amplifiers (PAs) is presented. The proposed mixed-signal predistorter (MSPD) is based on FIR memory polynomial (FIR-MP) model, where digital FIR filter improves the memory correction performance without any bandwidth expansion and the MP predistorter in analog baseband provides superior linearization. MSPD avoids 5X bandwidth requirement for the transmitter and the power-hungry RF components when compared to digital predistorters (DPDs) and analog-RF predistorters (ARFPDs), respectively. This makes the MSPD solution a very low-power candidate and especially attractive in the context of small-cell base stations. Extracted PA model of a commercial 1 W GaAs HBT PA is linearized over an 80 MHz signal; results prove that the FIR-MP based MSPD in ideal system-level simulations provides an improvement of 14.3 dB and 13.5 dB, in adjacent and alternate channel leakage ratio, ACLR1 and ACLR2, respectively, in comparison with FIR envelope memory polynomial (FIR-EMP) model, used in ARFPD. The impact of various non-idealities are simulated at electrical-level to derive the requirements for the integrated circuit implementation shows that a resolution of 8 bits for the coefficients and a signal path SNR of 60 dB is required to achieve ACLR1 above 45 dBc, with as little as 9 coefficients in the analog domain.