| 摘要 |
PURPOSE: A ring detection circuit is provided to detect a ring signal quickly by converting the ring signal into an envelope. CONSTITUTION: When there is a ring signal, a capacitor(C1) removes a direct current from the ring signal, and applies an alternating current of the ring signal to a level limiter(110). The level limiter(110) limits a level of the ring signal, and outputs the limited ring signal to a photo coupler(120). The photo coupler(120) outputs the limited ring signal to the first integrator(130) by isolating an input side and an output side. The first integrator(130) and the second integrator(210) integrate the limited ring signal, and output an integration result of the limited ring signal to an invert part(220). The invert part(220) inverts the integration result of the limited ring signal, and outputs the inverted signal to a ring detection port of an MPU.
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