| 摘要 |
PURPOSE:To automatically stop the suppressing function of an echo suppressing circuit once the starting of transmission of a non-telephone signal is discriminated and until the ending is discriminated, by automatically discriminating the features of the non-telephone signal as a contrast to a telephone signal. CONSTITUTION:When a telephone signal a shown by a waveform (a) and a non- telephone signal B such as a PSK signal showing data arrive at the terminal 2 of a transmission line, an envelope detecting circuit 8 generates a signal (c) as an envelope and this is differentiated by a differentiating citcuit 10 to obtain a signal (d). This signal has a positive and a negative value quickly by turns in case of the telephone signal A, but becomes a rectangular signal in case of the non-telephone signal B and is supplied to a level comparing cirucit 13, where is compared with two threshold values L1 and L2 from a level threshold supplying circuit 12 to send an output (e) of 1, 0, or -1 to a time comparing circuit 16. When the continuation time of 1 and 0 is longer than a certain value, an output signal (g) is obtained and ORed with a signal (h) based upon the signal at the input terminal 4 of a reception side, so that an echo suppressing citcuit 1 is disabled by a singal (i). |
