Evaluation of the high-frequency small-signal performance of bipolar transistors under avalanche conditions

The S-parameters of discrete silicon bipolar microwave transistors have been measured at various collector-emitter voltages above and below the collector-emitter breakdown voltage (typically referred to as BV _ce0) in order to verify the influence of avalanche multiplication on the small-signal parameters (such as f_t and f_max). It was found that the small-signal device parameters are not adversely affected even when the DC characteristics deviate from the nominal behavior. The existing models for f_t and f_max are therefore valid provided that the operating point is accurately defined