COMMON-BASE TRANSISTOR EQUIVALENT CIRCUITS FOR WIDEBAND AMPLIFICATION

摘要

The problem of choosing a transistor equivalent circuit of practical usefulness for wideband, low-pass (video) ampli¬fiers is studied experimentally. Measurements of amplitude and phase response up to and beyond a cutoff are made on a single transistor in the grounded-base, resistance-loaded configuration. The calculated responses of several equivalent circuits of varying complexities are compared with the actual measured response. A simple T circuit, having collector capacitance and a single pole expression for a as frequency dependent elements, is found to fit the measurements as well as some of the more complicated forms. Approximate formulas are then found, which enable the cutoff frequency of such an am¬plifier to be calculated for all values of source and load resistance.