Method and apparatus including a novel DC-coupled junctor circuit for signaling across a solid-state crosspoint matrix network. The junctor comprises a pair of serially connected diodes interposed between the crosspoint network paths. A constant current source (or sink) is coupled to the junction of the diodes to provide a common DC current path therethrough for current coupled through the junctor diodes and the corresponding crosspoint paths and controlled variable impedance networks coupled thereto. Signaling across the solid-state crosspoint network is accomplished by selectively varying the impedance of one of the controlled variable impedance networks responsive to certain conditions being monitored in the interface circuitry associated with the crosspoint path by a corresponding loop supervision circuit. The resultant imbalance in current through the junctor diodes causes corresponding variations in the DC potential at the other crosspoint path output terminal which are monitored to control the interface circuitry coupled thereto. In an embodiment of the invention, the novel junctor circuit is employed in an electronic private automatic branch telephone exchange (EPABX).

Low-level, wide-band signals e.g. for use in telephone transmission are switched in a matrix device. The overall matrix is subdivided into elementary matrices of smaller size and each inlet of the overall matrix is provided with a selector for selecting the appropriate elementary matrix which contains the desired cross-point. This subdivision is performed as is conventional to reduce interference and attenuation from echos generated in the unused portions of the matrix, but it has the drawback of increasing the complexity of switch control, two selectors and one cross-point needing activation in the place of a single cross-point. The present invention provides selectors which are sensitive to the conductive state of the cross-points to which they are directly connected to repeat the conductive condition to their respective inlet of the overall matrix, thereby simplifying switching control without sacrificing transmission characteristics.

The invention relates to a diode switch for the optional switch-through of an input-end signal to an output, in which two diodes, poled oppositely to one another, are arranged in the series arm and a third diode is arranged in the shunt arm of a four-pole, and wherein the different switching states are determined by the conductive state of the oppositely poled diodes and of the third diode, with a simultaneous blockage of the particular other diodes. The four-pole is preceded by an impedance transformer having a very low output resistance and is followed by a transformer having a very high input resistance. A first constant current source having a current strength of J.sub.1 /2 is connected after the output of the series arm diode; a second constant current source having a current strength of J.sub.1 is connected to the nodal point of the diode with a polarity which is such that the oppositely poled diodes are each traversed by a current having a strength of J.sub.1 /2. On the disconnection of the second constant current source, a third constant current source is connected to the nodal point with a polarity which is such that the shunt arm diode is traversed by its current. Following the output and series arm diode during the connection of a third constant current source a blocking voltage is connected which is substantially matched to a bias voltage occurring at the output of the input and impedance transformer.

A common control, multi-station, multi-conversation path intercom system using a single stage, crosspoint matrix for effecting the switching between stations. Two digit dialling, either multifrequency tone or dial pulse is used to control the switching to a called party. Each station line circuit has a talking potential supply and a current control network. The conversation link circuit provides a choke coil isolating talking currents from the talking battery. Each matrix crosspoint has a plural transistor network for performing its switching through function.