| 摘要 |
A telephone line interface circuit comprises two unity gain d.c. amplifiers (132, 134) having outputs d.c. coupled via feed resistors to the line wires. Currents in the feed resistors are monitored via a digital control circuit (152), which can be programmed to provide desired operating conditions. The control circuit controls, via D-A converters (158, 160), currents passed by current sources (142, 148) through resistors (140, 146) at inputs of the d.c. amplifiers, thereby determining voltages at the amplifier inputs and hence on the line wires. These d.c. voltages are smoothed by capacitors (136, 138) used for coupling an a.c. signal to the d.c. amplifiers. The voltage control facilitates adaptive adjustment of the line interface circuit to the line in dependence upon the monitored currents.
|
