Silicon planar epitaxial transistors as fast and reliable low-level switches

This paper attempts to accentuate all the salient factors of high-quality switches, such as their static properties, stability under various conditions of high temperature or thermal cycling, and some aspects of their transient response. It is shown that the silicon planar epitaxial transistor possesses the most advantageous combination of properites for general application as a low-level switch, and that simple low-injection level formulas are sufficiently accurate for the calculation of voltage offset and resistance of an "on" switch, as well as the "off" resistance, if extrinsic parameters and current dependence of βnand βiare taken into account. A simplified procedure is proposed for the selection of temperature-compensated switch pairs. Hysteresis in a single parameter βnis shown to be the main cause of instability in voltage offset in germanium alloy-type transistors, an effect which is hardly detectable in silicon planar epitaxial devices. Suitability of the latter for fast operation in chopper amplifiers is discussed, and their capabilities in a rapid-sampling commutator is illustrated.