An Analog Linearizer for Doherty Amplifiers Based on Impedance Modulation

This paper presents an analog linearizer for Doherty amplifiers (DPAs) to accurately compensate for gain curves with multiple inflection points. The linearizer consists of a hybrid coupler and two Schottky diode nonlinear networks, one of which is used to achieve a gain trend with a single point of inflection, while the other further increases the number of inflection points through impedance modulation between branches. By sweeping its bias voltages, the proposed linearizer has a flexible tunable gain range and a low phase variation. Excited by a single carrier 64‐QAM signal with a bandwidth of 20 MHz, the test results show that the proposed linearizer is able to effectively compensate the AM−AM of DPA at 3.5 GHz without deterioration of AM−PM. The output adjacent channel leakage ratio (ACLR) of the example DPA is improved by 5 dB, from −32.8/−32.6 to −40.8/−41.1 dBc, and the error vector magnitude (EVM) is improved from −29.4 dB to −37.9 dB.