Fully Electronic Space-Division Telephone Exchanges Using Semiconductor Crosspoints and Optical Switching

The state of the art in fully electronic space-division telephone exchanges shows that neither can semiconductor crosspoints directly replace reed relay contacts in Public exchanges, nor can hitherto semiconductor switching networks compete with reed relay switching networks. Though semiconductor crosspoints fulfill all transmission requirements, they are too expensive. Investigations on this field by the authors led to the following results. 1) A semiconductor crosspoint with high breakdown voltage and low on-resistance has been developed. This crosspoint can be connected to a subscriber´s line and thus directly replace a reed relay in a public exchange at only slightly higher cost. 2) These crosspoints with high voltage capability can be combined with low cost, low breakdown voltage MOS semiconductor arrays in large-scale integration (LSI) techniques which are isolated from the subscriber lines by transformers to form a fully electronic switching network. 3) A crosspoint free of on-attenuation which can be monolithically integrated to crosspoint arrays has been developed; 4) A thick-film hybrid crosspoint for switching of commercial high-resolution video signals has been developed. The state of the art of optical switching systems shows that switching networks using a laser beam enable the transmission of wideband video signals with comparatively high crosstalk attenuation.