| 摘要 |
PURPOSE:To transmit a smooth polarity inversion signal without using any LC circuit by connecting a filter comprising a resistor and a capacitor to a two-way constant current circuit in a subscriber circuit of an exchange to constitute an electronically formed inductance. CONSTITUTION:The electronically formed inductance circuit is constituted by connecting a filter circuit comprising a resistor R3 and a capacitor C to a 2-way constant current circuit comprising transistors (TRs) Q1, Q2 in DC feeding circuits 1A, 1B. Variable voltage sources 2A, 2B are made up of power booster TRs Q3, Q4 and an operational amplifier OPA, and the level of a control signal fed to input terminals 3A, 3B is inverted to transmit a polarity inverting signal to a subscriber TEL. Even if the TRs Q1, Q2 are turned off at the same time at polarity inversion, resistance division circuits R1, R2 are connected, the AC impedance is kept to a constant value and no noise/distortion takes place. |
