| 摘要 |
PURPOSE:To identify call tone and busy tone, by binarizing and differentiating an audible wave input signal, counting it at an up-down counter and comparing the output with upper and lower threshold value, in a signal detection system of a digital terminal station device using an audio analysis and synthesis system. CONSTITUTION:When an audible wave signal tone is inputted, a signal binarizing the intermission of signals with an integration binarizing circuit 3 is formed, and initial set is made for an up-down counter 5 with a differentiated 4 differentiated pulse. Counting is made with clocks from a clock input terminal 16 until the next differentiation pulse comes, the output of the counter 5 is compared with an upper threshold value 16 with a comparison circuit I6 and with a lower limit threshold value 17 at a comparison circuit II7. The output of a call tone is high level and the output of a busy tone is a low level from the result. By using a monostable multivibrator 12, AND circuit 13, and FFs 10, 11, initial set identification can be made without malfunction due to noise. |
