A simple method to extract intrinsic and extrinsic base-collector capacitances of bipolar transistors

A new and direct method is proposed to determine intrinsic (C_μ) and extrinsic (C_μx) base-collector junction capacitances of bipolar junction transistors (BJTs). The voltage dependent curves of C_μ and C_μx are obtained by using a new Y-parameter equation that is derived from a simplified "cut-off mode" equivalent circuit including ac current crowding capacitance. This new method is superior to several conventional ones, because it remains valid when there is ac emitter current crowding. The superiority of the new method has been verified by observing much better agreement of modeled gain with measured ones than the conventional method.