Patent GB-1004511-A (GB)
Title: Electronic switching network
IPC: H03K17/70
Filed: 1961-10-09
Abstract: 1,004,511. Automatic exchange systems. AUTOMATIC ELECTRIC LABORATORIES Inc. Oct, 9, 1961 [March 20, 1961], No. 36233/61. Heading H4K. In an arrangement for testing for free paths through a switching network comprising a plurality of nodes interconnected by stages of bi-stable switching elements, a marking potential applied to a first stage, switches one of the elements to extend the marking to the next stage and so on until it reaches a point marked busy or until it reaches an unmarked node, whereupon the testing reverts to a preceding node, and continues from there until either all paths have been tested or a marked node at the last stage is reached. Fig. 1 illustrates the principle of operation. A +25 v. marking potential applied to node 61 causes one crosspoint element, say 11, to fire. This lowers the potential of node 61 so that 12 cannot fire. Condenser C 1  charges up and the potential of node 71 rises to cause either 13 or 14 to fire. These being biased at - 26 v. fire before 12 can, since the latter is only biased at - 20 v. Say switch 13 fires, then C 3  charges up until node 71 reaches a potential to cause 14 to fire. Switch 13 is now back-biased and switches off. When C4 charges up the potential ef node 71 rises, and with C3 and C4 charged 13 and 14 do not switch again, so the potential of node 71 and consequently of 61 rises sufficiently to fire switch 12. This back-biases 11 which switches off. Testing then proceeds over switches 15, 16 and when the last test has been made, say over switch 16, this switch extinguishes too when C 6  charges up, R6 being high. Thus at the end of the test capacitors at the nodes of all free paths are positively charged. If now an outlet T2 is marked at - 30 v. it effects breakdown of all the switches 27, 1,6, 12 in the path to T1 and the resistances of the now completed series path over the switches assumes a near earth potential. Alternatively the terminal T2 may be marked before T1, progressive testing from T1 taking place as before until the path to T2 is struck whereupon the path assumes near-earth potential to inhibit further testing. Nodes may be accessible from other inlets similar to T1, and if busy in another connection, the nodes will be at earth potential to prevent the firing of switches leading to them, so that a path through that nodee is not indicated. In one embodiment, Fig. 4 (not shown), the marking potentials are applied via transistors, and when the path is struck one of the transistors is cut off, the other providing a sustaining current for the switches until the connection is to be broken. In a second embodiment, Fig. 5 (not shown), the progressive marking operation is initiated from both sides of the network. Thus the marking from one side is first allowed to charge capacitors at nodes in all idle paths up to a certain central stage. Then the marking is applied to the other side until and the progressive marking continues until at the central switching stage condensers on each side of one of the switches are charged (with opposite polarity) so firing the switch to complete the connection. In further embodiments intermediate junctors are provided. In one such embodiment, Fig. 6 (not shown), fan out occurs from each marked terminal towards the junctors which are then scanned for coincidence of markings from each side, one such being enabled when found. In another such embodiment progressive marking occurs from each junctor when it is scanned, Fig. 7 (not shown). In a further embodiment, Fig. 8 (not shown), on each side of the junctor as it is scanned simultaneous fanout from the marked terminal and the junctor takes place. In an alternative arrangement a plurality of junctors may simultaneously produce a fan-out for a number of stages on either side of the junctor. Progressive marking is then initiated from a marked terminal on each side towards the junctors, and a junctor which can establish connection on both sides is then taken into use. The bi-stable switches may be gas diodes or form layer diodes. The switches may, however, be provided with control electrodes for improving their switching characteristics. Specifications 813,862, 850,214 and 963,454 are referred to.