| 摘要 |
PROBLEM TO BE SOLVED: To provide a subscriber circuit incorporating a speech current polarity changeover circuit without increasing the circuit scale. SOLUTION: Since an output stage circuit 5b of a DC feedback circuit 5 and an output stage circuit 6b of an offset cancellation circuit 6 are configured the same, a signal fed back to an input of a balanced amplifier 4 is switched by using a switch 7 to select an input voltage to the circuits so as to invert the polarity of the speech current. Furthermore, it is not required to add any specific circuit for speech current polarity changeover and the circuit not requiring a dielectric strength such as the switch 7 is configured by a CMOS, then the circuit scale is reduced. |
