New pi equivalent circuit for high-frequency bipolar transistors

A procedure is presented for determining a simplified equivalent-circuit model for a shallow n-p-n integrated bipolar transistor with a transition frequency of approximately 2.5 GHz. The modified hybrid-pi equivalent-circuit model used to represent this transistor is shown to be a very poor representation at microwave frequencies, and an equivalent circuit is derived which has the whole common-base output capacitance placed between the base terminal and the collector junction. The condition is given under which this simplified equivalent circuit is valid.