Semiconductor Circuit Design Philosophy for the Central Control of an Electronic Switching System

The proper selection of semiconductor switching circuits to be employed in electronic switching systems is influenced by a large number of different factors. Some of these are the result of systems philosophy, 1 while others are concerned with device availability, required reliability, economy and ease of design, manufacture and maintenance, etc. We do not propose to go through an exhaustive design analysis of the circuits described herein, but we shall present the techniques which were developed. The particular experimental electronic switching system of interest here operates with a stored program in real time and in a generally synchronous serial mode, utilizing direct-coupled (dc) logic. The largest concentration of semiconductor circuitry is in the central control of the system, which is the data and information processing center of the telephone central office. It is with the circuits in the central control that this paper is mainly concerned. In most present-day electromechanical switching systems many operations take place in parallel, due to the speed limitations of relay circuits. Electronic switching systems also can be built using the parallel 1125