Analog Linearization of a 10-W GaN Power Amplifier by Baseband Feedback

This work presents an experimental investigation on power amplifier (PA) linearization using baseband feedback (BBF). The technique takes advantage of the even-order intermodulation tones produced at the baseband frequencies, which are proportional to the envelope amplitude of the radio-frequency (RF) input signal. These components are fed from the drain terminal to the gate terminal of the transistor of the considered single-stage PA. A suitable gain and phase shift are applied to minimize the third-order intermodulation products (IMD3) across the entire input power sweep range up to compression. The experimental results, carried out on a 10-W Gallium Nitride (GaN) High-Electron-Mobility Transistor (HEMT) proof-of-concept prototype, demonstrate improvements of up to 18 dBc in the in-band IMD3 for various tone spacings from 5 MHz to 20 MHz. In addition, the method shows a 3-dBc improvement in the Adjacent-Channel Power Ratio (ACPR) and 1% reduction in Error-Vector Magnitude (EVM) for a 1-MHz 16-QAM signal.