| 摘要 |
PURPOSE:To detect a tone signal by a simple circuit even when the number of kinds of tone signals to be detected is large by reading a stored detection signal regarding a frequency out of an address corresponding to the counted value of a counting circuit. CONSTITUTION:The tone signal of frequency (i) from an input terminal 1 is inputted and compared by a level decision device 3 with a reference level signal (c) from a reference level generator 4. When the signal (a) is larger than the signal (c), a reset signal (d) is reset and the counting circuit 7 becomes ready to count. At the same time, an (n)-cycle segmenting circuit 2 detects the period of (n) cycles of the signal and holds the signal (b) at H level only in (n) cycles. A reference clock generator 5 outputs a reference clock signal (e) and an AND gate 6 ANDs the signals (e) and (b), which is gated and counted as a count clock signal (f) by the circuit 7 to generate a counted value signal, so that the signal is supplied as an address input to a ROM 8. For the purpose, address data are set in addresses of a ROM 8 to detect plural tones of frequencies i1, i2....
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