Trunk interface circuit with current compensation

摘要

A trunk interface circuit useful for remotely terminating a two-wire central office trunk at a remote telephone facility includes a current compensated miniature transformer. The transformer includes windings for coupling voice band signals between the trunk and the remote telephone facility and a compensating winding for reducing d.c. flux associated with supervisory d.c. current applied to the trunk at the central office. A circuit connected with first and second portions of a first transformer winding provides signal indication of magnitude and either of two possible directions of current flow in the first winding. A bidirectional current regulation circuit conducts a compensating current in either of two directions in the compensating winding. The compensating current is regulated in accordance with the signal indication from the circuit connected with the first winding to reduce the d.c. flux in the transformer. The signal indication is also used by a supervisory signal detector to couple supervisory information to the remote telephone facility.