A Bridge for Measuring Audio-Frequency Transistor Parameters

A bridge is described which measures the small-signal parameters of point contact and junction transistors at a frequency of 1 kc. The impedance parameters of point-contact transistors are measured for the grounded-base connection, while a set of parameters representing a compromise between the impedance parameters and the h parameters is measured for junction transistors operating in either the grounded-base or grounded-emitter connections. This set includes the short-circuit input impedance h11, the short circuit current amplification factor h2l, a paralleled resistance r22 and capacitance C22 representing the open-circuit output impedance, and two feedback resistances r12 and r12' which in the particular case of the grounded-base connection represent the "low-frequency" base resistance rb and the "high-frequency" base resistance rb' respectively. It is also shown that the α cut-off frequency of junction transistors can be calculated with good accuracy from the bridge measurements.