Design for linearizability of GaN based multi-carrier Doherty power amplifier through bias optimization

In this paper, a GaN based symmetrical Doherty power amplifier is designed. The Doherty amplifier bias conditions are optimized for a trade-off between power added efficiency and linearity. The carrier amplifier is biased for linearity and the peaking amplifier bias is chosen for maximum power added efficiency. Measurement results under a four carrier WCDMA drive signal show respectively 43% power added efficiency and -32.5dBc adjacent channel leakage ratio at 6dB output power back-off. Linearization of the designed Doherty PA using baseband digital predistortion led to quasi perfect cancellation of spectrum regrowth while operating at an output power back-off equal to the input signal's peak to average power ratio.