INTERMODULATION MECHANISM AND LINEARIZATION OF ALGAAS GAAS HBTS/

The intermodulation (IM) mechanism of heterojunction bipolar transisto rs (HBT's) has been studied by using an analytical nonlinear equivalen t circuit model and Volterra-series analysis of the model, Although th e third-order IM intercept point (IP3) does not depend-on the emitter parameter, it is appreciably affected by base and collector parameters and has been substantially improved by utilizing punchthrough collect or structure. The measured IP3 of punchthrough collector HBT's is 31 d Bm with 150-mW de power, which is higher than that of normal collector HBT's by 3 dB. The investigation of the cancellation effects of nonli near elements reveals that the output nonlinear current components gen erated by emitter-base current source and base-collector current sourc e cancel each other almost exactly, resulting in high linear character istics of HBT's.