| 摘要 |
<p>PURPOSE:To prevent the mixture of an induced common-mode signal such as a broadcast radio wave as a common-mode signal to high frequencies and a differential signal to a low impedace by connecting an HPF to the reference input of a constant current circuit so as to drive a constant current circuit. CONSTITUTION:When the low frequency of a telephone voice band is inputted, the input signal is smoothed by capacitors CA0, CB0 having a large capacitance and inputted to constant current circuits 3, 4. Thus, a sufficiently high impedance is given to both the lines A, B at the telephone voice band. If an induced common-mode signal is mixed as the radio wave of a medium wave broadcast, capacitors CA1, CB1 of the HPFs 1, 2 are low in the impedance. As a result, the constant current circuits 3, 4 are controlled by said induced common-mode signal and the circuits have a low AC impedance. Moreover, a low impedance is also attained for the differential signal.</p> |
