Analysis and design optimisation for inverse Class-F GaN Doherty amplifier

An analytical model of an inverse Class-F (Class-F-1) Doherty power amplifier (DPA) with a proposed compensation method is presented. The derived model was shown to be effective in predicting the behaviour of the fundamental current and optimum load impedance in both a carrier and peaking cell for a Class F-1 DPA. Based on the analysis results, the degradation of the RF performance, including the peak output power, efficiency, and linearity, caused by an inherent lower current driving of a peaking cell is also proven. To compensate this issue, a dynamic gate bias for a peaking cell using a proposed voltage shaping is introduced. For verification, a 2.4 GHz GaN Class-F-1 DPA was designed and fabricated. Using the proposed gate shaping method, improvements of the maximum output power of 2.6 dB and peak power drain efficiency of 5.6% are achieved compared with a conventional case. With a 10 MHz 6.5 dB peak-to-average power ratio signal, the Class-F-1 DPA achieves an average output power of 36 dBm with a DE of 54% at a 28 V supply voltage. The measured adjacent channel rejection ration under such conditions is below -30 dBc.