A Design Approach for Two Stages GaN MMIC PAs With High Efficiency and Excellent Linearity

A novel design methodology for two stages microwave monolithic integrated circuit (MMIC) power amplifier (PA) is presented. The proposed solution allows to almost null the phase distortions (AM/PM) without worsening other key features of the PA, such as amplitude distortion (AM/AM) and efficiency. The derived approach is verified presenting the design and the experimental characterization of a two stages GaN MMIC PA for Microwave Backhaul radio links. The MMIC has been developed in a commercial 0.25 mu m GaN power process, resulting in a 3 x 3 mm(2) chip area. At 7 GHz, the realized module shows 6 W of saturated output power, 17 dB of gain, 63% of power added efficiency and less than 1.5 degree of phase distortion. Moreover, when tested with modulated signals (i.e., 256 QAM modulation scheme, 7 dB of PAPR), the PA shows a spectral regrow lower than at 32 dBm of average output power without any predistortion, while the average efficiency is around 30%.