Extended Efficiency Range, Equal-Cell Doherty Amplifier Design Using Explicit Circuit Model

This letter presents the design of a symmetrical Doherty power amplifier (DPA) with extended high-efficiency range by using a new and explicit circuit model. Theoretical analysis reveals that by the adjustment of the electrical length of transmission line sections in the proposed circuit model, new DPA variants with simple circuitry and enhanced output back-off (OBO) are obtained. For experimental verification, a 42-dBm, 2-GHz DPA with OBO of 9.5 dB was designed and fabricated using identical GaN HEMT devices. Under continuous-wave stimulation, measurement results indicate good Doherty behavior can be obtained with 9.5-dB back-off efficiency of 51%-61% and saturation efficiency of 68%-72% over 1.85-2.1 GHz. Moreover, with single carrier WCDMA signal (centered at 2.1 GHz) and peak-to-average power ratio of 9.6 dB, the proposed design is found to deliver an average drain efficiency of 58% and adjacent channel leakage power of -47 dBc at an output power level of 32.5 dBm.