| 摘要 |
PURPOSE:To make it possible to obtain excellent call quality by lowering the sidetone of a SLT (single line telephone set) by constituting a sidetone erasing circuit on a silicon wafer. CONSTITUTION:When the handset of a SLT connected with a terminal T and a R point is raised for the purpose of a call, the current by power source circuits 1, 18 flows between the terminal T and the R point via the SLT, while a power source transistor for IC 17 is turned on and an IC for subscriber line starts to operate. The signal from the SLT is received in a reception circuit 4, passes a sidetone erasing circuit 5 and is transmitted to a terminal a. The signal from a terminal b passes through an amplifier circuit 3 and a drive circuit 2, becomes current modulation by the power source circuits 1, 18 and is transmitted to the SLT. At this point, the signal transmitted to the SLT from the terminal b returns to the sidetone erasing circuit 5 after the signal becomes the transmission signal from the SLT, is cancelled by the signal adjusted by a balance circuit 7 and does not appear in the terminal a. |
