Line interface circuit

Claim 1

A line interface circuit for energizing tip and ring leads of a communication line with direct current from a power source and for coupling alternating current signals between the communication line and a hybrid circuit associated with a telephone facility, with a characteristic impedance substantially corresponding to a predetermined impedance comprising: tip and ring terminals for connection to the tip and ring lead; first and second battery terminals for connection to the power source; tip and ring feed resistors each connected to respective one of the battery terminals, the tip and ring feed resistors being of similar ohmic values; a transformer having tip and ring primary windings being connected in series between the tip terminal and the tip feed resistor and the ring terminal and the ring feed resistor respectively, said tip and ring primary windings so connected being poled such that a flow of energizing current is of a magnetically aiding effect in the transformer, the transformer also having a secondary winding for connection to the hybrid circuit; a resistive capacitive network being connected between the secondary winding and the hybrid circuit, and including, a capacitive reactance device connected to the secondary winding and being of a predetermined value, whereby voice band alternating currents in the primary winding are transformer coupled with a predetermined complex impedance, and a resistive element being connected serially with the capacitive reactance device and the hybrid circuit, and at least another resistive element being connected between the secondary winding and the hybrid circuit, the resistive elements being of values whereby the coupling of alternating current signals within a voice band range of frequencies is effected at said characteristic impedance.