An Experimental Solid-State Pulse Modulated Wideband Switch

Switching of wideband information on an analog basis is generally achieved by the use of switching arrays utilizing electromechanical crosspoints. This paper describes the results of a program initiated to investigate the possibility of designing an equivalent system utilizing solid-state devices. Investigations were carried out to determine the suitability of both solid-state space divided switching arrays and also into the use of time divided switching networks. It soon became obvious that with the high input frequencies that were required to be switched, the corresponding frame periods and time slot durations would require clock frequencies, rise times, etc., which were excessively fast for reliable working. It was, therefore, decided that space division techniques would be utilized. It was also decided that dependency on the use of amplitude modulated inputs would be avoided due to the susceptibility to interchannel crosstalk. This was especially critical at the higher frequencies contemplated, due to the increased effect of stray capacity. A review of various nonamplitude modulated pulse systems resulted in a choice being made to convert all amplitude dependent inputs into a pulse position code. This choice was based on economic factors together with the fact that even though it has an analog characteristic, it is generally insensitive to amplitude variations. The resultant plan, therefore, evolved into a space division switching system utilizing the conversion of all inputs into a pulse position code.