A Method for Designing a Linear, Efficient 2-Stage GaN PA for Supply Modulation

This paper presents a simple design method for reducing the distortion from large positive phase slopes observed in supply modulated GaN PAs, while keeping the gain magnitude flat. The proposed method utilizes the driver stage in a 2-stage design to compensate for most of the phase change. The phase response of the driver has negative phase slope at fixed low gate biases versus input power. Co-optimizing driver bias and the final stage drain modulation function achieves close to flat gain magnitude and phase. A demo- and a reference PA are supply modulated with the same function and measured with a 5MS/s 16-QAM signal, giving Po,avg=36dBm and PAE>53.3%. The demo PA’s gain magnitude and phase ripple are less than ±0.25dB and ±2.0deg. respectively, with EVM=2.4% and ACPR=-42.3dBc. The reference PA’s gain magnitude and phase ripple is ±0.75dB and ±12.0deg. respectively, with EVM=5.12% and ACPR=-32.5dBc.