Patent GB-938684-A (GB)
Title: Electrical switching matrix
IPC: H03K17/62
Filed: 1960-07-08
Abstract: 938,684. Automatic exchange systems. STANDARD TELEPHONES & CABLES Ltd. July 8, 1960 [July 13, 1959], No. 23950/63. Class 40 (4). Each of the cross-point switching devices in a switching matrix is switched on or off according to the state of an individually associated bistable device, the bi-stable devices being arranged at the cross-points of a control matrix so as to be set or reset by coincident marks on row and column wires. As applied to the telephone network of Figs. 1A and 1B, subscribers A and B, a trunk circuit TK, and a circuit arbitrarily specified as N, are connected to the common row wires of the finder matrix, Fig. 1A, and the connector matrix, Fig. 1B. The column wires of each matrix terminate on link circuits 18, and 18a. Separate control wires P1 and P2 extend from the line or trunk circuits to the finder and connector matrices, respectively, to provide row wires of control matrices the cross-points of which are coupled by double-base diodes, otherwise termed unijunction transistors, such as 6 and 8. A calling line or trunk circuit is detected by a scanner 17 and a free link circuit is held ready for service by marking the associated column control wire of the finder matrix from an allotter 19. The calling condition extends a mark to the control wire P1 to the finder matrix and causes conduction in the normally non-conductive doublebase diode at the intersection of the wire P1 and the column wire marked from the allotter. Since the diode is bi-stable it holds conductive when the marks are lifted from the control wires and by altering the base bias of the symmetrical transistor comprising the switching device at the cross-point of the switching matrix causes this to conduct and connects the calling line to the link. The link returns dial tone, accepts dialled digits, causes the wanted line circuit or trunk to extend a mark on its control wire P2 to the connector matrix, and marks the column control wire peculiar to itself in the connector matrix. As a consequence the marked double-base diode in the connector takes up its conductive state and holds the associated crosspoint transistor conducting to connect the wanted circuit to the link which connects it back to the calling subscriber. Release of the connection is effected from the link which momentarily breaks the path to the emitter of the conducting double-base diode and sets it back to the non-conductive state. The allotter, when connected as shown to mark the vertical control wires of the finder matrix, cannot allot the next link circuit until the cross point has been set up. If such marking is effected from the link the allotter may be released sooner. Bi-stable germanium transistors, termed Thyristors, may be employed in place of double-base diodes as the bi-stable devices which may each control two associated cross-point switching devices in go and return paths over a matrix providing for the interconnection of 4-wire lines. When enabling a connection a bi-stable device may back-bias diodes to lock out the bi-stable devices in the occupied row and column of the matrix. Specification 938,685 is referred to.