| 摘要 |
PURPOSE: To improve the accuracy and stability of the power to be supplied to a subscriber's line by respectively connecting the cathode of a diode and a Zener diode to the output terminal of a third operational amplifier and a constant-current generator. CONSTITUTION: An output stage for telephone interface circuit is provided with a pair of operational amplifiers A1 and A2 and the noninverted input terminals of the amplifiers A1 and A2 are respectively connected to the output terminal of a third operational amplifier A3 and a signal source S. The noninverted input terminal of the amplifier A3 is coupled with a reference voltage Ve REF through a constant-current generator IP. The noninverted input terminal of the amplifier A2 of the amplifier pair A1 and A2 is connected to the first terminal of a supply voltage generator through a current generator which supplies a current proportional to the current flowing to a first resistor R1 and, at the same time, to the second terminal of the supply voltage generator through a third resistor R3 . In this output stage, a fourth resistor R4 is connected between the inverted input terminal of the amplifier A3 and the constant-current generator IP and a diode D1 and a Zener diode DZ are connected in series between the output terminal of the amplifier A3 and the generator IP. Therefore, a constant supply voltage is supplied to a subscriber's line with higher accuracy than the conventional example from a monolithic integrated circuit type output stage for telephone interface circuit between the subscriber's line and the controller of an exchange. |
