GB1194479A - Improvements in or relating to Time Division Multiplex Circuits - Google Patents

Abstract

1,194,479. Automatic exchange systems. STANDARD TELEPHONES & CABLES Ltd. 10 April, 1968, No. 17378/68. Heading H4K. In a telephone exchange employing time division multiplex transmission over a highway separate portions of each time position in the multiplex cycle are used for conveying speech, for supervising the condition of the highway, and for receiving signals from the highway. The arrangement shown is similar to that used in Specification 1,155,805, and shows transistor cross-points VT1 and VT3 in successive switching matrices. The connecting path is routed through these cross-points by simultaneously biasing the bases of these transistors to conduction. The time slots are separated by short pauses during which inhibiting signals BS4 are applied to a gate G3 which normally passes the biasing pulses XS. This ensures that the crosspoint switches such as VT1 are closed during the inter-channel pause and allows a pulse BS5 to be applied to line via a transistor VT6 so as to discharge the line as described in the abovementioned Specification. The cross-point VT3 is closed during the inter-channel period by the inhibit pulse BS4 and during the supervisory and signalling periods by timing pulses BS7 and BS8, respectively. These are short duration pulses timed to occur at different instants near the beginning and within the active portion of each time position. Each time the transistor VT3 is blocked by the pulses BS7 and BS8 (while the transistor VT1 is conducting) current drawn to the highway causes a transistor VT5 to switch to saturated conduction connecting the line to a pair of gates G1 and G2. The gate G1 is opened by the first pulse BS7 during the supervisory period while gate G2 is opened by the second pulse BS8 during the signalling period. Tone signals Ts may be applied to line via a transistor VT7.