Patent GB-822297-A (GB)
Title: Improvements in or relating to electrical switching circuits
Inventor: WRIGHT ESMOND PHILIP GOODWIN
IPC: H04J3/20
Filed: 1956-06-05
Abstract: 822,297. Automatic exchange systems. STANDARD TELEPHONES & CABLES Ltd. May 31, 1957 [June 5, 1956], No. 17395/56. Class 40 (4). To effect a connection between subscribers allocated different time channels in a pulse multiplex system the information represented by the modulation of a pulse train of one time channel is stored and then read out to form a modulated pulse train of the other time channel. Storage may be effected by means of capacitors or ferro-magnetic cores. As shown in Fig. 1, speech signals on a line A are repeatedly connected to a time division multiplex highway MH at one time position by a gate GA in coincidence with the connection of a capacitor CS to the highway by a gate GS over inductors L1 and L2. A capacitor CA terminates the line A and with inductors L1, L2, and capacitor CS forms a circuit with a time constant such that the charge on CA is completely discharged into CS during the time gates GA, GS, are open. At a second time position gates GB and GS are repeatedly opened so that the charge on CS is discharged into capacitor CB of a low-pass filter which terminates line B and reconstitutes the speech from line A. If the circuits CA, L1, L2, CS, and CB, L1, L2, CS, are each symmetrical the arrangement transmits speech in both directions. Additional storage capacitors CS1 and gates GS1 may be connected to accommodate further connections over the highway, each connection involving the seizure of a free storage capacitor. As shown in Fig. 3, the invention is applied to an exchange, such as described in Specification 765,681, to interconnect groups of subscribers P to V. Each group is served by a multiplex highway such as H1 or H2 and each highway can be connected to another over links LP to LV by gates such as 3G4, 3G5, and storage capacitors CP to CV. If line x of group P is to be connected to line y of group V, a free time channel is seized in highway H1 and gate 3G1 is repeatedly opened at this time. In response to digits dialled by the calling subscriber gate 3G4 is also repeatedly opened at this time to connect line x to the link LV associated with the group V. A free time channel is seized in the highway H2 of group V and thereafter gates 3G5 and 3G7 are opened repeatedly thereafter at that time. Gate 3G6 associated with storage capacitor CV serving the link LV is repeatedly opened at both channel times, being thereby alternately connected to lines x and y. A number of capacitors may serve each link. The gates in both Figs. 1 and 3 may be symmetrical junction transistors controlled from stores recording the identity and seized time positions of the calling and called lines. Fig. 5 shows a ferromagnetic storage core which may replace the storage capacitors. Assuming the core is at maximum remanence a speech-modulated pulse on terminal 51X is applied over gate 51G during a time interval PG1 to set the core in accordance with the energy of the pulse. During a later time interval PF3 a gate 52G is opened in coincidence with the opening of a gate 53G and the application of a read-out pulse from terminal 54X to reset the core. The modulated pulse is thereby regenerated and passed to terminal 52X. Transmission of modulated pulses in both directions between terminals 51X, 52X, can be achieved by resetting the core during an initial part of the interval PG1 by means of a pulse on terminal 53X and setting it during a latter part. The core is then reset during an initial part of the interval PF3 and set by a pulse on terminal 54X during the latter part. Specifications 644,570 and 780,831 also are referred to.