Frequency Variations of Current-Amplification Factor for Junction Transistors

In a grounded-emitter or grounded-collector connection of a junction transistor, the effective current amplification is proportional to the factor (1-α)-1, where α is the current-amplification factor of the transistor. As a result of the phase shift associated with a, the magnitude of (1-α)-1 decreases rapidly with increasing frequency. It is shown that the magnitude of (1-α)-1 is 3 db below its low-frequency value at a frequency of the order of magnitude of (1-α₀) times the frequency at which the magnitude of α alone has decreased 3 db below its low-frequency value of α₀. In addition, experimental results of measurements of phase and amplitude characteristics of α as a function of frequency for several fused-impurity p-n-p junction transistors are presented and are compared with the variation of α with frequency calculated in accordance with the theory of Shockley, et al.