| 摘要 |
PURPOSE:To attain ease of identification with an external call tone and a dial tone of other telephone sets by providing a control circuit controlling the operating state of an oscillator in response to a rectifying/smoothing voltage and a discharge circuit discharging the rectified/smoothed voltage at a high speed. CONSTITUTION:A tone ringer circuit 13 receiving a call signal rectifies and smoothes the signal and gives a voltage VB to a control circuit 21. An oscillator 22 generating a signal VC and outputting a prescribed voice signal VD when the voltage VB reaches a high level is operated by the circuit 21, which stops the oscillation when the voltage reaches a low level threshold value. The voltage VB decreases further even when the value is lowered than the low level threshold value, but its voltage level is compared with a reference voltage Vref by an operational amplifier 31 and when Vref>VB, a transistor Q1 is driven to lower the voltage VB at a high speed. The circuit is actuated similarly when the input is a dial pulse and the call tone and the dial tone are discriminated easily. |
