Cold Cathode Gas Tubes for Telephone Switching Systems

Gas discharge tubes have found extensive use in telephone switching and other digital systems. Most of these applications take advantage of the fact t h a t both switching and memory can be provided by a single gas discharge device. T h e switching characteristics result from the fact t h a t the device is an essentially open circuit when the gas is not ionized and a closed circuit when the gas is ionized. The memory function is possible because the t u b e can be held in a high current condition, once it is ionized, by a voltage which is too low to initiate this conduction. T h u s a triggering signal which ionizes the tube is "remembered" until the holding voltage is removed and the t u b e is allowed to de-ionize. In some applications, gas tubes are used as switching devices in series with voice frequency circuits. For this purpose, the t u b e must offer a low impedance to audio frequency signals in addition to meeting requirements of switching and memory. This paper first describes some switching characteristics of gas tubes considered as circuit elements. Desirable performance objectives are established in terms of these device characteristics. Following this, physical processes within t h e t u b e are described as they relate to circuit per755