Distribution of the Collector Resistance of Planar Bipolar Transistors: Impact on Small Signal Characteristics and Compact Modeling

We investigate the relevance of the distribution of the extrinsic collector resistance of a bipolar transistor with respect to its small signal characteristics. We show that this distribution is relevant to the admittance parameters in general and to the cut-off frequency and unilateral power gain in particular. We present analytical results for ;y-parameters in terms of elements of the small-signal equivalent circuit of the Mextram compact model, extended with distributed extrinsic collector resistance. Hence, our results are relevant to compact modeling, bipolar device technology development and characterization and to design of RF power amplifiers.