Simple General Analysis of Amplifier Devices with Emritter, Control, and Collector Functions

The comparative signal amplifying capabilities of lumped solid-state and vacuum tube devices of the emitter-control-collector type are described in a very simple, yet general, manner in terms of charge control, charge storage, and charge motion. The emitter-collector charge transit time is shown to be a ubiquitous physical parameter determining current, voltage, and power amplifications and their bandwidth products. Also of central importance is a characteristic capacitance that describes the capability of the inter-electrode space to store mobile charge. The unipolar and analog transistors, the grid-controlled vacuum tube, and the beam deflection tube all have characteristic capacitances approximately equal to their electrode geometrical capacitances. The bipolar transistor holds an advantage over the other solid-state devices because it can have a larger characteristic capacitance. This advantage also holds against the vacuum tube devices, but is tempered by the fact that the latter can have much larger carrier drift velocities. For the solid-state devices it is emphasized that the saturated carrier drift velocity is sometimes a better indication of material merit than carrier mobility. Ultra-high frequency performance of the solid-state devices requires some combination of microscopic dimensions, improved materials, or charge multiplication.