Switching circuits using bi-directional non-linear impedances

Abstract

In a brief general review of logic circuitry, a case is developed for a bi-directional, non-linear switching element. In order to compare circuits using such elements with those using standard semiconductor diodes, the main features of diode gates are considered in detail. Particular attention is paid to design of p-n-p transistor driver stages and their dependence on the logic sequence. Circuits using a bidirectional ?constant voltage? element are described, including a ?two-decision? AND gate. Possible types of constant voltage element are discussed and experimental results are given for multi-electrode silicon carbide devices. An interesting feature of the latter is the non-linear behaviour of capacitance. An attempt is made to compare gating circuits employing constant voltage, bi-directional elements with standard diode gates from a performance/cost point of view. A ?majority-logic? gate is made possible by a ?constant current,? bidirectional element. If one input is used as a control, this gate can become a many function gate, thus a 3-input gate can be controlled to act as a 3-AND, an OR, or a ?2 or more out of 3? logical unit without change of input or output connections. Some possible realisations of the constant current device are discusssed. A binary-octal decoder circuit and a simple binary full adder circuit are given as examples of the application of the non-linear elements and to illustrate their unusual features.