Patent GB-904231-A (GB)
Title: Four-wire two-wire converter
IPC: H04Q11/04
Filed: 1959-03-13
Abstract: 904,231. Automatic - exchange systems. STANDARD TELEPHONES & CABLES Ltd. March 13, 1959 [March 18, 1958], No. 8807/59. Class 40 (4). A four-wire/two-wire converter circuit comprises a tuned storage circuit L, C, Fig. 1, arranged to be connected by gates G1, G2, G3, respectively, with the incoming circuit H1, the bi-directional circuit H2 and the outgoing circuit H3. The gates G1, G2, G3 are pulsed in cyclic order and energy transfer takes place on a tuned circuit bases during the pulses. Thus, during the pulse t1 energy is transferred from a tuned circuit connected to H1 to the capacitor C of the tuned circuit C, L. During the pulse t2 this energy is then interchanged with that stored in a tuned circuit connected to H2, and during pulse t3 the energy on C, L is transferred to a tuned circuit connected to H3. The duration of the pulses is equal to half the period of the tuned circuits to ensure complete transfer of energy. Circuits H1, H2, H3 may be multiplex highways, H2 being connected through further gates to tuned circuits connected to subscriber's lines via low-pass filters. Two such converters per channel may be used for amplifying the pulses in a both-way multiplex system WH2, EH2, Fig. 2. Thus, converters CGW, CGE connect the both-way multiplex systems to two interconnected oneway multiplex systems having respective amplifiers A1, A2. In the event that the restriction on the timing of the pulses proves irksome a further gate and tuned storage circuit may be included between H1 and G1, the further gate enabling the storage circuit to accept energy at a convenient time position from H1 and releasing it at time t1, via gate G1. The time positions tl, t2, t3 may be evenly spread over the cycle of such positions used for the multiplex working or may occupy consecutive time positions. In this latter case a combination of three converters only as shown in Fig. 3, may suffice for the whole multiplex cycle. The references to the gates have two-digit suffixes, the first digit representing the phase of the time position at which it was opened. Thus, for the first channel H1 is connected by G11 to L1C1 at time position number 1. At time position number 2, L1C1 interchanges energy with H2 via G22. At time position number 3, L1C1 passes its energy via G33 to H3. The second channel uses C3L3 similarly and the third channel uses C2L2. The store L1C1 is now free for use by the fourth channel and so on. Fig. 4 illustrates an electronic exchange utilizing the invention. Subscribers line circuits LC incorporating low-pass fiters and tuned storage circuits are connected by gates LG to the twoway group highways GH and thence to an intergroup highway IGH by group gates GG. From the intergroup highway further gates such as GG give access to other group highways connected by gates like LG to other subscribers. Local connections are effected by simultaneously pulsing all relevant gates for interchange of energy between the storage circuits of the subscribers. Intermediate pulse positionchanging equipment using a reactive store may be used. Incoming calls over four-wire interchange lines such as IJ are connected via combined low-pass filters and tuned circuits MF1, MF2 to converter units CG1 for connection to a subscriber LC over both-way multiplex highways GH, IGH, IH. Outgoing calls are similarly connected over GH, IGH and OH to outgoing junctions OJ. Transit calls may be effected via the both-way highway IGH or over separate pairs of one-way multiplex highways WH, EH. Pulse code modulation may be used and pulse position changing incorporated at the incoming end of the junction, reactive stores being provided into which the signals are gated by signals synchronized with those of the originating exchange and gated out by pulses synchronized with those used at the terminating exchange. Specifications 753,645, 822,297 and 824,221 are referred to.