DTMF signal receiving apparatus equipped with a DTMF signal judging circuit

摘要

A DTMF signal receiving apparatus includes a DTMF signal receiver; and a DTMF signal judging circuit. The DTMF signal receiver includes an input section for receiving an input signal from an external apparatus; a plurality of first band-pass filters connected to the input section; a plurality of second band-pass filters connected to the input section; and an output section connected to the plurality of the first band-pass filters and the plurality of the second band-pass filters, for outputting a code based on a plurality of outputs from the plurality of the first band-pass filters and the plurality of the second band-pass filters. The DTMF signal judging circuit includes a first judging device connected to the plurality of the first band-pass filters, for outputting a first judgment signal based on a plurality of first outputs from the plurality of the first band-pass filters; a second judging device connected to the plurality of the second band-pass filters, for outputting a second judgment signal based on a plurality of second outputs from the plurality of the second band-pass filters; and a third judging device for judging whether the input signal is a DTMF signal or not based on the first judgment signal and the second judgment signal and for permitting the output section to output the code when judging that the input signal is a DTMF signal.