| 摘要 |
PURPOSE:To prevent the deterioration in quality of call due to level contrast, by reducing the amount of loss of one variable amplifying circuit by the amount corresponding to echo erasion, through the output of a detection circuit estimating the amount of erasion of echo. CONSTITUTION:When a signal comes from two-wire side at the E side, an echo erasing circuit 12 is operated to cancel the amount of echo produced at two/four- wire conversion point 4, the amount of echo erasion is estimated at an echo erasing amount detection circuit 20 and control is made so that the amount of loss of a variable gain amplifying circuit 6' at the W side can be reduced within the amount of erasion. When a call signal comes also to the W side from this state, the output of the circuit 20 is held. Next, when call is by the W side only, the circuit 6' at the W side becomes the gain and the circuit 5' becomes the loss and the loss of the circuit 5' can be reduced by the range of the amount of erasion. Thus, the loss inserted to the opposing side can be reduced to the same gain as that toward call with the amount of erasion. |
