| 摘要 |
PURPOSE:To simplify a circuit configuration and to decrease the area of the integrated circuit by separating an inputted DTMF signal into a high group frequency component and a low group frequency component, converting a reception tone signal into a rectangular wave signal, inputting a pulse signal and discriminating a tone frequency being a specific frequency. CONSTITUTION:A sinusoidal wave tone signal passing through, e.g. a high group BPF 1 is inputted to a comparator circuit 3, where the signal is converted into a rectangular wave and the converted signal is outputted to a pulse generating circuit 5. A counter 7 uses a pulse signal inputted from the circuit 5 as a reset signal for a binary counter. Then the count is increased for each period of the counter clock signal inputted separately and the count corresponding to the time interval of the pulse signal is outputted. A count inputted from the counter 7 is decoded in a decoder 9 and only a specific frequency signal corresponding to the count is detected and outputted among high group frequencies fH1-fH4. |
