A Pulsed Load Modulation (PLM) Power Amplifier with 0.35μm pHEMT Technology

A new modulation scheme, namely pulsed load modulation (PLM), for high efficiency power amplification has been introduced. In PLM scheme, the concept of switched resonator is utilized to modulate the load impedance of a power amplifier in a digital fashion so as to maintain maximum efficiency and linearity. In this paper, a 1.87 GHz high efficiency PLM power amplifier is presented. The power amplifier module is implemented with two 0.35 mum GaAs pHEMT devices from Triquint Semiconductor and a bandpass filter centered at 1.87 GHz. The measurement is done at 1.87 GHz carrier frequency with 10V supply voltage and 384 Mbps, 1.1V gate switching voltage. The testing results show a maximum of 72.5% drain efficiency and maximum 30.21 dBm output power. A maximum of 60.9 % Drain efficiency is achieved at selected power level with diplexer included. Comparing with an ideal class B mode power amplifier, the improvement of power efficiency under power back off level of 6.4 dB and 8.1 dB are 40% and 50% respectively. An Envelope Delta Sigma Modulation (EDSM) version of WCDMA signal is used for the system linearity test.