| 摘要 |
PURPOSE:To make it difficult for malfunction to occur, which is caused by the peripheral noise of a transmission/reception call switching circuit by comparing a call input inputted through a microphone with a low pass call input through an LPF so as to discriminate the peripheral noise. CONSTITUTION:Where a voice is added, the level ration of an LF call input level passing through the LPF 20 to that before passing is raised because of a low loss level. In case of only a noise the level ration becomes high due to a high cut ration by the LPF 20. Accordingly the sound of a threshold setting circuit 22 and the reference level of the noise discrimination are set, and a level comparator circuit 23 compares them so as to discriminate the sound from the noise. Here, when the output of the comparator circuit 23 is 'H', it is discriminated to be a voice, and therefore an analog switch 24 is turned on to input the call input to a comparator circuit 13, whereby the normal transmission/reception call switching is executed. On the other hand, when the output of the circuit 23 is 'L', the transmission call input form a microphone 1 is judged to be the peripheral noise to turn off the switch 24, and the transmission call level is not inputted to the circuit 13, thereby preventing malfunction.
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