| 摘要 |
PURPOSE:To prevent a talking from being cut off temporarily at off-hook of a subscriber terminal device by connecting an externally mounted resistor to an output terminal of an operational amplifier and connecting a capacitor between a positive terminal of the said amplifier and a power supply. CONSTITUTION:A 2-wire side of a hybrid circuit HYB conducting 2/4-wire conversion is connected to an inverting input of operational amplifiers OP1, OP2 resistors R4, R5 and resistors R3, R5 are connected between the inverting input and an output terminal as feedback resistors R3, R5. Further, resistors Rf1, Rf2 are connected between the inverting input of the amplifiers OP1, OP2 and connecting points between resistors R1, R2 and constant cuttent soruces CI1, CI2 capacitors Cf1, Cf2 are connected in parallel with the constant current sources CI1, CI2 and connected to the negative terminals of the amplifiers OP1, OP2, then the problem of charge/discharge of the capacitors Cf1, Cf2 is eliminated because of the on-hook and off-hook of the subscriber terminal device T. |
