A Baseband Feedback Approach to Linearization of a UHF Power Amplifier

This work presents a power amplifier (PA) linearization approach based on baseband feedback. The modulated signal envelope is fed back from the transistor's drain to its gate with an applied amplitude and phase shift selected to reduce the intermodulation distortion (IMD3) product at the output. The design targets IMD3 improvement near the PA's 1-dB compression point (P1dB), enabling linear operation at a higher output power level and therefore improved device periphery utilization and efficiency. This approach offers a potential linearization alternative to digital pre-distortion, which cannot be applied in some systems, without affecting the RF performance. The 850-MHz proof-of-concept prototype based on a 15-W GaN device is characterized with a two-tone measurement with 5-MHz spacing, and demonstrates 9-dB improvement of the lower IMD3 tone near the P1dB point.