GB1153912A - Improvements in or relating to Electronic Switching Networks - Google Patents

Abstract

1,153,912. Automatic exchanger. SIEMENS A.G. 13 Jan., 1967 [14 Jan., 1966], No. 1903/67. Heading H4K. In a multistage-cross-point switching network marking potentials upon co-ordinate marking wires switch a cross-point four-layer transistor via a coincidence circuit at that cross-point. The provision of holding current for the transistor enables the marking potentials to be removed. In one arrangement the coincidence circuit comprises a resistor and two diodes each connected to one marking wire; in another arrangement a transistor is used having its base and emitter receiving marking potentials and its collector connected to the base of the crosspoint transistor. However in the arrangement shown in Fig. 7 where a subscriber T13 is connected to a connector Vs over cross-point fourlayer transistors KP1, KP2 and KP3, four-layer transistors SV are used as the coincidence circuits. Marking potentials Um1 and Um2 from co-ordinate marker wires render the transistors SV conductive to supply base current to the cross-point transistors KP which flows from this transistor over R4 or in the case of the first cross-point over Rt. The cross-point transistors are held by a current from source U1 in Vs when switch S closes, permitting the marking potentials to be removed. When neither transistor SV or KP at a cross-point is conducting the U10 source upon the p-doped emitter of SV produces a potential across the diode formed by the n and p doped base regions which as applied to the base of transistor KP reduces the capacitance of this base region and thereby the transistor's ability to conduct in response to interference pulses applied to the emitter from another connection path in the network. In other arrangements a separate diode is provided in the coincidence circuit for this purpose. The transistors AV, which are non-conductive when holding current flows in the connection path, indicate the state of seizure of the stages of the path. Diode SD2 or resistor Rs protect other transistors SV from overloading by source U10. The connection path provided by the crosspoints is broken down and crosspoints opened by cutting or reducing the holding current, such as by opening switch S or opening one crosspoint or by injecting a negative pulse into the path. A two-wire connection path is described (Figs. 8 and 9, not shown) where a pair of fourlayer transistors at a cross-point are switched by a single coincidence circuit comprising a three-layer transistor having one or two collectors connected to both or one of the crosspoint transistors. The formation of the switching network as integrated circuits is mentioned.