Line circuit for a telephone system having optical solid state means

1,167,741. Telephone exchange systems. WESTERN ELECTRIC CO. Inc. 5 Oct., 1966 [12 Oct., 1965], No. 44452/66. Heading H4K. [Also in Division G1] In a circuit for connecting a subscriber line to a switching network photon-coupling is provided in each direction of transmission. An arrangement for a two-wire line, Fig. 4, includes gallium diodes 60, 62, photon-coupled to photonresponsive transistors 64, 66, and diodes 52, 54 photon-coupled to transistors 50, 56 for the reverse direction. A differential amplifier is provided to prevent the singing which would arise from the series elements 50, 60, 62, 56, and a feedback network 82 controls operating levels. The switching network 92 which includes crossed groups of three conductors is controlled by a network 80 marking a desired sleeve in response to a central controller 78 which is fed with information by line and trunk scanners 76, 90. An arrangement for connecting a four-wire sub-line to a switching network is described with reference to Fig. 5 (not shown).