| 摘要 |
<p>PURPOSE:To suppress the subscriber line in-phase current even if a DC potential applied to a TIP and a RING line is different by detecting an AC potential to be superposed and both DC potentials of a subscriber line, cutting off the respective DC potential, adding the AC potential so as to feed back only the AC component to a feed circuit. CONSTITUTION:The polarity of the AC potential applied to the TIP line is amplified inversely by an amplifier OP4 of a detecting circuit DETT detecting the DC potential of the TIP line of the subscriber line and the AC potential superposed on it. This is similar to the RING line. The potentials are applied respectively to a capacitor C in an AC component selecting circuit CX. Thus, the DC component is cut off, only the AC component is inputted to the amplifier OP6, its output is fed back to operational amplifier circuits AT, AR, so as to reduce the impedance viewing the left side feed circuit from a point alpha of the TIP line and from a beta point on the RING line. Thus, the in-phase current applied externally is suppressed.</p> |
