Distortion-cancellation of GaAs-HBT amplifier using bias-voltage droop control

Presented is a simple design method to improve the linearity of (heterojunction) bipolar junction transistor (HBT or BJT) power amplifiers (PAs) designed in the class-AB or B mode. The introduced approach controls the dynamic drooping characteristic of the base-emitter DC bias-voltage of HBTs as input power increases, resulting in correcting the nonlinear AM-AM and AM-PM conversions. Measurements for the demonstrated single-stage GaAs-HBT PAs with 29 dBm saturated output power show 6.5 dB improvement in the adjacent channel power ratio (ACPR) at 15 dBm average output power and 0.6 dB increase of the linear output power where the ACPR crosses -40 dBc.