Broadband linearization of InGaP/GaAs HBT power amplifier

High linearity over a broad frequency band is a requirement in many RF amplifier designs. This paper shows that adding low impedance terminations at the envelope frequency (ω₂-ω₁) to the input of a Gallium Arsenide (GaAs) Heterojunction Bipolar Transistor (HBT) Distributed Amplifier (DA) improves the third order output intercept point (OIP3) over a bandwidth of 0.5 GHz to 3 GHz by up to 7.4 dB. Furthermore, OIP3 can be increased up to 19.2 dB above P_1dB. Results show that the improvement in OIP3 comes without lowering gain, return loss or P_1dB. Simulation and measurement results also show that the optimum termination is a short circuit with a small capacitive reactance at the envelope frequency. By varying the frequency spacing (Δω) from 1 MHz to 50 MHz, the resulting variation in OIP3 after the addition of the traps is less than 7%.