A subscriber-line interface circuit (SLIC) has tip and ring amplifiers connected
to the tip and ring lines, respectively, of customer premises equipment (CPE).
The SLIC returns the ringing signal (provided to the CPE from a power supply connected
to the CPE's ring line), to ground or to battery, through the SLIC's tip amplifier.
In one embodiment, the SLIC has three switches: S1 connecting the power supply
to the ring line, S2 connecting the ring amp to the ring line, and S3 connecting
the tip amp to the tip line. During ringing, S1 and S3 are closed to return the
ringing signal to ground through the tip amp, which is preferably driven to saturation
during ringing to reduce power consumption. By eliminating the fourth switch that
appears in prior-art SLICs (e.g., connecting the tip line to ground), SLICs of
the present invention can be smaller and therefore less expensive to implement.
