This paper presents a frequency-selective RF vector predistortion linearization system for RF multicarrier power amplifiers (PAs) affected by strong differential memory effects. Differential memory effects can be revealed in two-tone experiment by the divergence for increasing tone-spacing of the vector Volterra coefficients 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 linearization requirements of the interband and inband intermodulation products of both the lower and upper sidebands. Theoretical verification of the algorithms are demonstrated with MATLAB simulations using a Volterra/Wiener PA model with memory effects. The baseband linearization algorithm is next implemented in a field-programmable gate array and experimentally investigated for the linearization 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 intermodulation products is demonstrated. Adjacent channel leakage ratio of up to 45 dBc for inband and interband are demonstrated experimentally at twice the typical fractional bandwidth.

Abstract-This paper presents a new architecture for the frequency-selective digital predistortion (DPD) for two-and three-band power amplifier (PA) linearization. Also, largely spaced-signal DPD using a digital intermediate frequency (IF) technique is demonstrated. The algorithm used accounts for differential memory effects up to fifth order for bands that can be arbitrarily spaced. The simulation and experimental studies are performed using various signal sets; two-and three-band multitone signals with various tone spacing, band separation, and complementary cumulative distribution function. An improvement of 10 dB over third-order linearization is demonstrated in simulation for more than 20 dB of adjacent channel power ratio reduction. The test signal and the linearization algorithm were implemented on a field-programmable gate array. The linearization algorithm was applied to an RF amplifier at 700-900 MHz. For the two-band case, more than 15 dB on the in-band, 13 dB on the third, and 5 dB on the fifth intermodulation distortion (IMD) cancellation were achieved. For the three-band case, more than 12 dB of IMD cancellation was observed. For largely spaced signal DPD, more than 15 dB of IMD cancellation was achieved. In the three-band case, the linearization of intermodulation byproducts overlapping with the in-band distortion is found to be of critical importance.Index Terms-Digital predistortion (DPD), memory effect, multiband linearization, power amplifier (PA).

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