Linearity Enhancement of GaN Doherty Amplifier by Forward Gate Current Blocking Method
This paper investigates linearity enhancements in GaN based Doherty power amplifiers (DPA) with the implementation of forward gate current blocking. Using a simple p-n diode to limit gate current, both open loop and digitally pre-distorted (DPD) linearity for wideband, high peak to average ratio modulated signals, such as LTE, are improved. Forward gate current blocking (FCB) is compatible with normally-on III-V HEMT technology where positive gate current is observed which results in nonlinear operation of RF transistor. By blocking positive gate current, waveform clipping is mitigated at the device gate node. Consequently, through dynamic biasing, the effective gate bias at the transistor input is adjusted limiting the RF input signal peaks entering the non-linear regime of the gate Schottky diode inherent to GaN devices. The proposed technique demonstrates more than a 3 dBc improvement in DPD corrected linearity in adjacent channels when four 20 MHz LTE carriers are applied.