Efficiency enhancement and linearization of GaN PAs using reduced-bandwidth supply modulation

This paper demonstrates drain supply modulation for simultaneous efficiency enhancements and linearization. A power-envelope trajectory is used to reduce the slew-rate requirements on the dynamic supply of a supply-modulated PA. The measured 2-GHz PA is a harmonically tuned 10W GaN PA with CW peak output power of 40.3dB and peak PAE of 69%. Six different drain supply trajectories are investigated with a 16-QAM 4MSym/s signal. Envelope tracking (ET) for the peak efficiency trajectory results in an average PAE=42.1%, Pout=30.0dBm, EVM=9.6% with a required tracking bandwidth of 11-24MHz. Using a power-envelope trajectory further enhances PAE by 6 percentage points, increases the output power by 1.9dB, and results in slightly better linearity, with a significantly lower drain supply modulator (DSM) bandwidth of 4.5MHz. Additionally, the strong gain variation with drain supply voltage characteristic of GaN devices is exploited to linearize the amplifier. A constant gain trajectory of 10.4dB results in average PAE=52.7%, Pout=33.7dBm, EVM=4.8% and a DSM bandwidth of 10-35MHz. The corresponding power-envelope trajectory results in the same performance, but requires only 4.5MHz DSM bandwidth. A 10MHz LTE test signal is also evaluated having similar results as the QAM signal.