A high efficiency WCDMA power amplifier with Pulsed Load Modulation (PLM)

A GaAs pHEMT power amplifier module designed for Pulsed Load Modulation (PLM) technique on Envelope Delta Sigma Modulation (EDSM) transmitter architecture is developed in this work. The dynamic impedance behavior origin from PLM technique provides efficiency enhancement and linear power modulation simultaneously. Comparing with conventional Class B mode power amplification, efficiency profile versus power back-off level is significantly improved. The system linearity for complex modulation signals is obtained through pulse based coding schemes and filtering in EDSM architecture. In this paper, a 1.87 GHz PLM power amplifier module is fabricated and tested. The testing results show a maximum of 59.5% drain efficiency and maximum 29 dBm output power including 0.8 dB output filter loss for constant envelope signal. Comparing to conventional Class-B mode operation, the PLM technique offered improved power efficiency by 57.4% at 6 dB power back-off and 76.9% at 10 dB power back-off. The PLM amplifier module has been tested by WCDMA signal with 10.8 dB peak to average power Ratio (PAR). At the output power of 26.3 dBm, the amplifier has achieved 43% power added efficiency (PAE) and 39 dBc ACLR at 5 MHz offset without using any additional linearization techniques. If the filter loss is removed from the efficiency calculation, the actual achieved PAE by the PA is above 50%.