Patent GB-1536452-A (GB)
Title: Electronic telephone switching equipment
IPC: H04Q3/52
Filed: 1976-04-21
Abstract: 1536452 Automatic exchange systems L'ELECTRONIQUE APPLIQUEE 21 April 1976 [21 April 1975] 16028/76 Heading H4K In a telephone switching system comprising a plurality of subscriber's circuits, a plurality of external line connecting circuits, an electronic crosspoint switching matrix and a logical control unit for cyclically scanning the circuits and controlling the switching matrix, each column and row of the matrix comprises a conversation conductor and a cross-point activation conductor; each circuit has a two-wire to one-wire converter, each subscriber's circuit being connected to a respective row of the matrix and each external line circuit being connected to a respective cross-point; each subscriber's circuit has means for periodically pulsing its cross-point activation conductor in response to control signals from the logical control unit and each column is controlled by a cross-point selection control unit responding to control signals from the logical control unit. The general organization of the system is shown in Fig. 1a where AB 0 to m are subscriber's circuits, ER 0 to q are external, the circuits CB 0 to n+1 are cross-point selection control units and LOG is the logical control unit controlling circuits AB, ER and CB. Subscriber's circuit, Fig. 3.-It includes a twowire to one-wire converter T connected between a subscriber's set (partly shown) PAB1 and a conversation conductor Chl, an input VDAB1 for receiving a scan signal from control unit LOG in response to which the state of the circuit is transmitted on output SLE, a store MA for marking a call to the circuit, a relay K2 for applying a ringing current to the subscriber's set, an input TON1R for supplying a tone signal requesting the subscriber to break the existing conversation through store M1R and an output Sh1 connected to a respective row of the matrix. External line circuit, Fig. 4.-It includes a two-to-one-wire converter TR connected between an external line LRj and a matrix crosspoint CRj, relays KO1 and KO2 for detecting opposite polarity signalling currents in the line LRj, relay KO3 for detecting a call condition on the line, relay KO4 for transmitting dialling pulses from input CNj (from a cross-point) to the line and outputs SL, DS2, DS1 for transmitting information to the control unit LOG. Column control unit, CB, and cross-point, PC, Fig. 2.-Each cross-point comprises a thyristor Th connected across the row and column conversation conductors cv, ch respectively, with its trigger input connected to the activation conductors sv, sh through resistor r 1 and diodes d0 and d1; resistor r0 couples the trigger to the column conversation conductor CV. PCR is a crosspoint connected to a single external line circuit through CRj SRj. Each control unit CB includes an amplifier AMPI which triggers cross-point thyristor when a pulse is received at input IAT and the respective row activation conductor sh is pulsed, a constant voltage current source MPB which marks or frees a column depending on which of the inputs PB, LB is active and an input IO through which an operator may break into an established conversation; input TEF simulates a "fictitious thyristor" on conductor CV when only one thyristor is operated on a column, which is designed for two operating thyristors, i.e. when a connection request is made by a subscriber, until he is connected to the called subscriber; a conductor CV may receive signals for dialling request, backcall return and wait when the called party is engaged through input TON. Operation.-A subscriber wishing to make a call is connected to a free column by the control unit LOG when its calling condition has been detected, and dialling tone returned. The control unit LOG receives the dialled digits and determines whether the called subscriber is free or busy; if busy it returns the busy tone, if free it connects the called subscriber to the same column as the calling subscriber. When a subscriber wants a connection to an external line, indicated by a predetermined dialling code, he is initially connected to a first free column, and the control unit LOG after determining that it is an external call it searches for a second column with a cross-point connected to a free external line and then transfers the connection of the subscriber from the first to the second column. A special row of the matrix may be allocated to the operator's position, if provided, to enable her to break into existing conversations, by manually activating the input IO, Fig. 2, of a column control circuit CB.