Linear operation of a p-n-p-n tetrode

At the present time all p-n-p-n devices are used exclusively as switches. The p-n-p-n tetrode however, is also capable of operating as a linear amplifier. A model describing the operation of such a device as a semiconductor tetrode amplifier is presented. The equations characterizing this model are based on the physical structure of a commercially available silicon planar p-n-p-n tetrode; they are used 1) to derive the device terminal characteristics, 2) to synthesize small-signal equivalent circuits suitable for low-frequency operation (h-parameter circuit) and for high-frequency operation (bridged hybrid-π circuit), 3) to study the dependence of short-circuit gains of the tetrode on the dc biasing currents and frequency, and 4) to obtain a stability condition which must be satisfied to insure that the operation of the device is restricted in its OFF state where it can function as a small-signal linear amplifier. The theoretical results are in close agreement with experimental values.