Patent GB-840921-A (GB)
Title: Time division multiplex telephone system
IPC: H04J3/00
Filed: 1956-08-16
Abstract: 840,921. Automatic exchange systems. AUTOMATIC ELECTRIC LABORATORIES Inc. Aug. 16, 1956 [Aug: 23, 19551, No. 25132/56. Class 40 (4). In a time division multiplex exchange comprising first and second groups of transmission paths, each of which paths has a capacitor connected thereto, a two-way highway is provided between the two groups of paths with gates between each first-group path and the highway and between each second-group path and the highway, trains of enabling pulses being applied coincidently to one gate of each group, the pulses being of opposite polarity and the gates including rectifiers so poled that the capacitors in the two paths concerned are charged and discharged, respectively, by the pulses, the arrangement being such that after the capacitors have assumed an equalizing potential, the pulse current is deflected at each gate from the capacitor to the highway. General description.-The exchange described caters for 100 subscribers, a calling subscriber being identified by marking circuits 340 and 360 which transfer its identity to one of ten pairs of calling tens and units registers, such as 810 and 830, assigned by a register distributer 910. The register pair controls the in-switching matrix 450 to connect the line to the highway SM460 during a time position allocated to that register pair. Ten link circuits such as 500 are individually assigned to the register pairs and are operated in the corresponding time positions to recover the signals of the calling lines from SM460. The link circuit assigned to the register pair receives the signals indicative of the wanted line and extends the connection over highway SM620 in the same time position. A ringing control matrix distributer 950 transfers the identity of the wanted line to the ringing control matrix 750 which tests the wanted line. The out-switching matrix 600 then connects the highway SM620 to the wanted line in the same time position to complete the connection, the wanted line being rung by ringing-machine 860. Initiation of a call at station 300.-Each of the one hundred substations includes a conventional telephone set, in which the dial impulse springs 317 are shunted by a resistor 318 and the off-normal springs 319. It is assumed that the register distributer 910 has allotted the idle No. 1 calling tens and units registers 810 and 830 to the tens and units marking circuits 340 and 360. Taking down the handset at station 300 changes the potential at the right-hand end of resistor 332B from ground to - 24 volts, at which it is clamped by the diode D327, whereupon transistor T329 conducts and applies - 24 volts to the cathode of D334 and the base of T338. Operation of marking circuits 340 and 360.- Each of these circuits has ten stages, of which only the first and last are shown in Fig. 3, the input lead of each stage of the tens marker 340 is multipled to the line circuits for which the tens digit corresponds to the stage number, e.g. LT-0 of the first stage is connected to all line circuits having the tens digit " 0." In the tens marker 340 the transistors T342-1 to T342-0 and T348-1 to T348-0 are normally conductive and T347-1 to T347-0 are normally non-conductive. In response to the marking on diode D334 of the line circuit 320 corresponding to directory number " 01," current flows in conductor LT-0 so that the junction of resistors 341A-0, 341B-0 and 341C-0 assumes- 24 volts thus biasing T347-0 conductive via resistor 341A-0 and D346-0, so that its collector and emitter assume- 24 volts. T342-0 and T348-0 become non-conductive, the former removing ground from its collector so that the current flow from the base of T347-0 passes via D349-0 and resistor 341C-0, and the latter rendering T352 conductive, thus extending ground potential to diodes D345-1 to D345-0 to provide a lower impedance path to LT-1 to LT-9 than is offerred by the non-conductive T347-1 to T347-9. Stage " 0 " is thus operated and the output conductor MT-0 is at - 24 volts. T338 conducts and its collector applies - 24 volts via conductor LU-1 (units digit " 1 ") to the " 1 " stage of units marker 360 wherein T367-1 conducts and T362-1 and T368-1 become non- conductive. Ground on the collector of T368-1 disables T367-2 and biases T368-2 non-conductive so that its collector assumes ground potential. This action proceeds along the chain of T368 transistors and all the associated T367 transistors are disabled. T372 then conducts and applies ground to the diodes D365-1 to D365-0. The - 24 volts at the emitter of T367-1 is applied to conductor MU-1. If more than one line in the tens group " 0 " is calling, more than one conductor LU will be marked, but as the stages of 360 can operate only one at a time with an order of preference from " 1 " to " 0," only one calling line will be identified at this time, the others having to await the release of marker circuits 340 and 360 by the line circuit concerned. Operation of calling registers 810 and 830.- When the register distributer 910 allots 810 and 830 to the marking circuits 340 and 360 it applies - 48 volts via the conductor BD1 to all the stages in 810 over resistors 817-1 to 817-0 and to all those in 830 over 843-1 to 843-0. In the tens register ground is applied over MT-1 to MT-9 to stages " 1 " to " 9 " and - 24 volts over MT-0 to the " 0 " stage, whereas in the units register 830 MU-1 applies - 24 volts to the " 1 " stage and MU-2 to MU-9 apply ground to the others. The resistors 817-1 to 817-0 and 843-1 to 843-0 connected to the lead RD-1 each have a value twice that of the resistors 816-1 to 816-0 and 838-1 to 838-0 connected to the leads MT-1 to MT-0 and MU-1 to MU-0. Thus the junction of 816-0 and 817-0 is at - 32 volts, whereas the corresponding points in the other stages of 810 are at less than - 24 volts. The sudden application of the - 32 volts to capacitor 820-0 causes a negative pulse to be applied to the base of T815-0, and to the collector of T813-0. T815-0 conducts and T813-0 follows suit, thus locking T815-0 conductive so that the anode of D821-0 is held at ground potential. Each pair of registers and the associated link circuit are allocated one time position in a cycle of ten such positions. To this end, the present registers being the No. 1 registers, a series of positive pulses PP1 of about 10 volts amplitude are applied from the pulse generator 850 to the anodes of D821-1 to D821-0, and pass via the forward biased D821-0 to conductor RT-0. Similar action takes place in stage " 1 " of 830 resulting in the forward biasing of D834-1 so that the pulses NP1 (negative pulses synchronized with PP1) applied to D834-1 to D834-0 pass via D834-1 to conductor RU-1. The RT and RU conductors extend to the inswitching matrix 450 to control operation of the cross-points therein. Operation of in-switching matrix 450.-The in-switching matrix 450 includes one hundred crosspoints corresponding to the lines of the exchange for connecting the calling lines to the highway SM460. A typical crosspoint consists of a pair of oppositely-poled diodes D404-1 and D405-1, a resistor 406-1 connected between their junction and a source of - 48 volts, and a transistor T403-1 having its collector connected to the junction of the two diodes and the resistor. The emitter is connected to the RT lead corresponding to the tens digit of the line concerned, and the base to the RU lead corresponding to its units digit, so that in the crosspoint referred to, which corresponds to the line 301, number " 01," the emitter is connected to RT-0 and the base to RU-1. The markings on these leads render T403-1 conductive during the periods of the pulses NP1 and PP1. Thus, if these pulses are of 5 Ásec. duration in each 50 Ásec. cycle, T403-1 conducts for 5 Ásec. out of each 50 Ásec. and current of the order of 30 ma. flows from its collector to the junction of D404-1 and D405-1. Initially, substantially all this current flows via D404-1, the secondary winding of TR-1 and the base-emitter path of T339 to - 24 volts. The negative voltage (-24 volts) assumed by the base of T339 is established across capacitor 336, and that assumed by its collector cuts off T329, thus removing - 24 volts from diode D334, whereupon T338 is cut-off. The marking circuits 340 and 360 are thus released. With 336 charged, D404-1 becomes non-conductive, and for the remainder of the pulse current flows in D405-1 to the highway SM460 which is multipled to the link circuits, including the link circuit 500, corresponding to registers 810 and 830, which is operated by the same negative pulses NP1 as are applied to 830. Operation of input control circuit 513 of link circuit 500.-Operation of any of the stages of registers 810 and 830 draws current through conductor 844 via the emitter-base path of T509, whereupon T513 conducts and cuts off T512 thus removing- 48 volts from IC-1 to mark the link circuit 500 busy to register distributer 910. The ground on the collector of T513 also renders T511 conductive, thus bring- ing T503 to its conduction threshold, so that when the pulses NP1 are applied to the emitter of T503 it conducts and a large current flows from the junction of D501-A and D501-B through its collector-emitter path. Initially, as substantially all the current from T403-1 flows to the line circuit 320, little current is supplied to D501-A, so that the current to T503 comes largely from ground via resistor 507, the primary winding of TR-2 and diode D501-B, so that capacitor 506A is charged to - 24 volts, and the calling line 301 is effectively connected via the signal transfer capacitors 336 and 506A to the No. 1 link circuit 500. The register distributer 910 is now operated to assign another pair of calling registers to the marking circuits. Operation of register distributer 910.-Assuming all the link circuits to be busy and that all the stages of the distributer 910 have been operated, the transistors T925-2 to T925-9, T927-2 to T927-