Subscriber telephone line interface circuit with reduced power stand-by mode

Claim 1

A subscriber telephone line interface circuit comprising first and second amplifiers of signals to be transmitted respectively to first and second subscriber line conductors, each amplifier having an input stage and an output stage, each output stage comprising first and second push-pull connected transistors connected to respective line conductors and supplied between first and second supply potentials common to the two output stages, said interface circuit further comprising a means for measuring the current in the line and a terminal for receiving a stand-by signal indicating that the circuit is to be placed in stand-by mode with a low power consumption, further comprising, responsive to reception of the stand-by signal: means for biasing the transistors of the output stages so as to establish a fixed potential difference between the line conductors connected to the transistors of the output stages; means for disconnecting the input stages from the output stages; and means for discontinuing the power supply for most of the elements of the circuit but not for the push-pull transistors of the output stages or the line current measuring circuit.