Effect of maximum power supply voltage on envelope tracking power amplifiers using GaN HEMTs

This work discusses wideband high efficiency envelope tracking (ET) power amplifiers using GaN high electron mobility transistors (HEMTs) to achieve high gain and high efficiency with good linearity. The performances of two ET amplifiers using the same GaN RF device and envelope voltages of 30-V peak and 45-V peak are compared experimentally. With the higher dynamic voltage swing (45-V case), a considerably higher PAE was obtained, as well as a higher gain. For a WCDMA signal with 7.7 dB peak-to-average ratio (PAR) and 3.84 MHz bandwidth, the 45-V peak envelope tracking amplifier shows an overall drain efficiency above 50 % at an average output power above 30 W and a gain of 13.7 dB. The result was achieved with a normalized RMS power error below 3 % and an ACPR1 of -45.2 dBc using memory-less digital predistortion. By comparison, the PAE achieved with the 30-V peak envelope tracking amplifier was 45 %, and the gain was 10.8 dB, with a similar linearity performance. The improved results can be understood on the basis of loss minimization from device on-resistance.