Approaches for Improving Efficiency: Adaptive Predistortion of Dual-Level Voltage Power Amplifiers

A stochastic approximation technique is presented as a low-complexity approach for improving efficiency by linearizing the power amplifier (PA) with dual-level supply voltage. The coefficients of the RF predistorter are updated by using the simultaneous perturbation stochastic approximation (SPSA) algorithm to minimize the adjacent channel power ratio (ACPR) under the transmit power constraints. The PA with a low supply voltage of 2 V can improve the efficiency by reducing DC power consumption in the lower output power range compared with the PA with a fixed supply voltage of 4 V. The efficiency of the PA can be further improved by using a combination of RF predistortion technique and dual-level supply voltage PA when operating close to a saturated region without significantly causing nonlinear distortion. The simulation results show that the RF predistorter using the SPSA algorithm has a faster convergence speed in suppressing spectral regrowth and a lower complexity calculation in the predistorter coefficient adaptation.