Frequency-selective predistortion linearization of RF power amplifiers

Abstract—This paper presents a frequency-selective RF vector predistortion linearization system for RF multicarrier power am-plifiers (PAs) affected by strong differential memory effects. Differ-ential memory effects can be revealed in two-tone experiment by the divergence for increasing tone-spacing of the vector Volterra coeffi-cients associated with the lower and upper intermodulations tones. Using large-signal vector measurement with a large-singal network analyzer, a class-AB LDMOS RF PA is demonstrated to exhibit a strong differential memory effect for modulation bandwidth above 0.3 MHz. New frequency-selective RF and baseband predistortion linearization algorithms are proposed to separately address the lin-earization requirements of the interband and inband intermodula-tion products of both the lower and upper sidebands. Theoretical verification of the algorithms are demonstrated with MATLAB simu-lations using a Volterra/Wiener PA model with memory effects. The baseband linearizationalgorithmisnext implemented inafield-pro-grammable gate array and experimentally investigated for the lin-earization of the class-AB LDMOS PA for two carrier wideband code-division multiple-access signals. The ability of the algorithm to selectively linearize the two interband and four inband intermod-ulation products is demonstrated. Adjacent channel leakage ratio of up to 45 dBc for inband and interband are demonstrated exper-imentally at twice the typical fractional bandwidth. Index Terms—Large-signal network analyzer (LSNA), lin-earization, memory effects, power amplifiers (PAs), predistortion, Volterra series