Advanced Design of Linear Doherty Amplifier for High Efficiency using Saturation Amplifier

We have developed a saturation Doherty amplifier which has higher efficiency than the conventional or linear Doherty amplifier. The proposed Doherty amplifier is based on the saturation amplifiers with the harmonic control circuit. We have analyzed the efficiency and the saturation operation of the amplifier related to the load modulation. To interpret the saturation operation according to the power level and harmonic cancellation mechanism, we have simulated the voltage and current waveforms and the IM3 amplitudes and phases of the carrier and peaking amplifiers. For verification, we have implemented the saturation Doherty power amplifier with inverse class F harmonic control circuit using Freescale MRF281SR1 LDMOSFET with a 4-W peak envelope power (PEP). For a 1-GHz forward-link WCDMA signal, the measured drain efficiency of the amplifier is 54.7%, and the measured adjacent channel leakage ratio (ACLR) is -29.4 dBc at an average output power of 32 dBm, while those of the comparable the inverse class F amplifier are 38.7% and -21.4 dBc at the same average output power level, respectively.