| 摘要 |
<p>A subscriber line interface circuit coupled between a telephone unit terminal and a switching system comprises a coding and decoding circuit (2) for controlling analog inputted (A1) and outputted (Ao) voltages with a direct current bias voltage (Vro) and an interface circuit (1) including means (7) for detecting said analog output voltage (Ao), means (6) for detecting a direct current bias voltage (Vr1) of said analog output voltage (Ao), substracting means (5) for determining the difference between said detected analog output voltage (Ao) and said detected bias voltage (Vro) and means (R1,R2) for driving the telephone unit terminal on the two-wire (2W) side, the analog voltage (Ao) and the direct current bias voltage (Vro) output terminals of said encoding and decoding circuit (2) being directly connected with the input terminal (Rx) of said analog outputted voltage detecting means (7) and the direct current bias voltage input terminal (Vr1) of said interface circuit (1), respectively whereby only desired alternating current signal is outputted to the telephone unit terminal on the two-wire side (2W). <IMAGE></p> |
