Electronic cross-point matrix telephone private switching equipment

Claim 1

A telephone private switching equipment comprising a plurality of subscriber's line circuits, a plurality of external network line connecting circuits, an intercommunication routing matrix for selective interconnection of the circuits of the said pluralities, said matrix being made of rows and columns having controllable electronic switch cross-points, and a logical control unit including means for ensuring a cyclical scanning of the free, occupied and communication request conditions of the circuits of the said pluralities and means responsive to communication request conditions detected in said circuits for controlling selective activations of electronic cross-points of the matrix performing the establishment of the requested communications, wherein: each column of the matrix comprises only a single conversation conductor and a single point activation conductor, each row of the matrix comprises only a single conversation conductor and a single cross-point activation conductor, each cross-point of the matrix comprises a single electronic switch member connected across the conversation conductors of a row and a column and having a trigger terminal connected by unidirectional leads to the cross-point activation conductors of said row and said column, each subscriber's line circuit and each external network line connecting circuit includes a two-wire to one-wire conversation converter having its one-wire terminal connected to the conversation conductor of a row in the matrix, each subscriber's line circuit includes means for periodically applying pulses to the cross-point activation conductor of the row to which it is connected, and, each column of the matrix is controlled from a cross-point selection control unit having first and second terminals respectively connected to the cross-point activation conductor and to the conversation conductor of the column, and including means for applying cross-point activation pulses to the first terminal, means for applying to said second terminal tone and switch bias electrical currents and means for applying to said second terminal in activated condition of a cross-point of the column a unidirectional constant voltage electrical current the path of which closes in the subscriber's line circuit.