| 摘要 |
A subscriber line interface circuit is provided that includes an output stage having a pair of differential transconductance amplifiers to drive the tip and ring lines of a telephone exchange. The output stage includes circuitry that advantageously reduces the power dissipated within the integrated circuit when the subscriber loop impedance is relatively low. As a result, heat generation within the integrated circuit is reduced. Circuit reliability may therefore be enhanced and fabrication and packaging costs may be reduced. In one embodiment, an off-chip resistor is coupled from an output line of the ring line amplifier to the negative voltage rail. When the loop impedance is low, a relatively large voltage drop is established across the resistor which therefore absorbs a greater percentage of the loop current. Since the resistor is provided off-chip and diverts current that would otherwise flow through the ring-line amplifier, the overall heat dissipated within the integrated circuit is reduced. |
