Two channel method for measuring the current gain of transistors at high frequencies

A method has been developed for measuring the common-emitter short-cicuit current gain of transistors at frequencies in the range 10¿500MHz. The measurement is made by comparing the voltage outputs of two parallel channels, one of which contains the transistor and a standard attenuator; at balance, the transistor gain equals the attenuator loss. The best absolute accuracy obtainable is within ±0.1 dB, but is limited in practice by the quality of available commercial attenuators to within about ± 0.2dB. The method is suitable either for accurate routine meaurements or to give a precise `go-no-go¿ indication of whether a required specification is met. The method has been realised in two versions, both using lumped components: a single-frequency version and a wideband version. The single-frequency version will accept transistors with long leads, and imposes no practical upper limits on the d.c. bias which may be applied. The wideband version is inherently less accurate as a result of stray cpacitance from the base terminal to earth; if the stray capcitance is regarded as an essential part of the transistor, the accuracy is not much less than that of the single-frequency version. The d.c. bias in the wideband version is fed through resistors, which may limit the maximum allowable current.