| 摘要 |
PURPOSE:To reduce the quantizing noise of an A/D converter by calculating the sum of squares of a false echo path to estimate the attenuation value of an echo signal, controlling gain in the A/D converter on the basis of the estimated value and then estimating the characteristics of the echo path again. CONSTITUTION:When the connection of a circuit is completed and its echo path is fixed, a switch 401, (4011-401n) is connected to the register 3 side, a switch 402 is connected to a subtractor 13 side and the conversion voltage range of an A/D converting circuit 404 is made at its maximum to perform the 1st estimation of the echo path. A false echo value L obtained by said estimation is latched by a controlling circuit 403 to perform the 2nd estimation of the echo path. At that time, the input voltage range of the A/D converter 404 is multiplied by L (L<=1) by a control signal C5 and quantizing step voltage is decreased as multiplied by L. A false echo signal y'(t) is subtracted by an echo signal y(t) by using the false echo path obtained by the 2nd estimation to cancel the echo signal. |
