A 330W Distortion-Cancelled Doherty 28V GaAs HJFET Amplifier with 42% Efficiency for W-CDMA Base Stations

An L/S-band 330W distortion-cancelled Doherty GaAs FET amplifier has been successfully developed optimizing the main and the peak amplifiers load impedance shift. The amplifier employed a pair of 28V operation 150W GaAs heterojunction FETs. It demonstrated low third order intermodulation of -37dBc with a drain efficiency of 42% at an output power of 49dBm around 6dB back-off level under the two-carrier W-CDMA signals of 2.135GHz and 2.145GHz. To our knowledge, these represent the best results ever reported among the simple high power FET amplifiers for W-CDMA base stations. Moreover, we proposed the evaluation techniques to obtain each AM-AM and AM-PM characteristics of the main and the peak amplifiers in an operating Doherty amplifier, and for the first time, experimentally proved the distortion cancellation effect in the GaAs FET Doherty amplifier