Simulation and modelling of a heterojunction bipolar transistor mixer

The first low-power HBT (heterojunction bipolar transistor) mixer intended for use in mobile communications equipment is described. Measured conversion gain and intermodulation performance superior to that of active MESFET mixers is reported. The HBT offers several advantages for personal communications receivers, including longer battery life, reduce IF (intermediate frequency) circuit complexity, and better adjacent channel interference properties. Both MESFET and HBT mixer conversion gain is a strong function of output resistance and transconductance; hence, the HBT offers better conversion gain. An analytical expression is derived which enables prediction of the conversion gain of an HBT mixer to be made. A computer program has been implemented which enables the user to assess the effect of model parameters and embedding impedances on conversion gain.<>