A monolithic telephone subscriber loop interface circuit

An integrated circuit that interfaces a subscriber loop with the digital telephone exchange has been produced with conventional high-voltage IC technology. The monolithic SLIC controls DC loop current, converts signal transmission from two-wire to four-wire, and suppresses longitudinal induction. Bias control circuitry automatically reduces standby power when subscriber equipment is detected on-hook. High-voltage circuit techniques maintain performance when the supply voltage exceeds the n-p-n transistor BV/SUB CE0/, and circuit partitioning with two discrete transistors yields manageable junction temperature and an economical 102/spl times/112 mil die size.