A Tri-Branch Analog Pre-Distortion Linearizer for the Compensation of Gain Inflection in Doherty Power Amplifiers

In this work, a novel tri-branch analog pre-distortion linearizer that compensates for the gain inflection within a Doherty power amplifier (DPAs) is presented (DAPD). This circuit features two non-linear branches using Schottky diodes whose expanding characteristics are used to compensate the gain and phase non-linearity caused by carrier PA compression within a DPA architecture. The DAPD was first designed and simulated using custom Schottky diode models, resulting in a circuit that is simple in its operation, featuring only two control voltages. Demonstrated in this work is the ability of the DAPD to linearize carrier PA compression, allowing for higher back-off efficiency to be achieved whilst maintaining linearity. This is illustrated through modulated signal measurements using 50 MHz 5G NR signals, where a correction of Adjacent Channel Power Ratio (ACPR) of between 6.5 - 9.3dB over a bandwidth of 2.2-2.6 GHz is achieved.