Investigations of linearity characteristics for large-emitter area gaas hbt power stages

In this paper the linearity properties of large-emitter-area GaAs heterojunction bipolar transistors are experimentally investigated. The approach is based on AM-AM and AM-PM conversion measurements, performed on-wafer with an active harmonic load-pull system. The measured data are then processed to evaluate the transistor linearity in terms of intermodulation distortion (IMD) and adjacent channel power ratio (ACPR). As an important result, the harmonic source impedance at the second harmonic plays a significant role in determining the maximum output power allowed for a given IMD or ACPR level