| 摘要 |
A RINGTRIP DETECTION CIRCUIT FOR USE ON TELEPHONE SYSTEMS The present invention implements a ringtrip circuit that compares the positive and negative energies of the ringing current. The term energy, as used here, implies total duration that the current is positive or negative. The current during ringing is sampled by a cycle detector. The positive and negative durations are measured by an up/down counter and compared to a known value by a comparator. Any DC shift in the current will begin increasing the difference between the positive cycle duration of ringing and the negative cycle. If the difference exceeds some number set forth in the logic, then a ring trip will occur. The sampling of the ringing current is performed with opto devices to maintain isolation from the digital portion of the circuit.
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