| 摘要 |
PURPOSE:To make small and highly reliable the unit, by detecting the tone signal at the digital circuit. CONSTITUTION:The input signal from the terminal 10 is digitized at the PCM coding circuit 11, and sin and cos components are calculated at the sin conversion circuit 12a and the cos conversion circuit 12b. After the output of the conversion circuits 12a, 12b is accumulated for a given time at the integration circuits 13a and 13b, it is squared at the square circuits 14a, 14b and added at the addition circuit 15. The discrimination circuit discriminates the frequency component in the input signal is within the specific level range, and receives the output of the addition circuit 15 and performs comparison of the specified lower limit and upper limit. When the frequency component of the input signal is at the middle of the specified upper and lower limit, the signal showing the reception of the specified tone is output to the output terminal 17. Thus, the tone detection circuit is integrated for the circuit and the reliability can be increased. |
