| 摘要 |
A dial pulse detection circuit for partial correction of grossly distorted line current dial pulses, which provides square wave output signals for use by later timing detection circuitry. To detect such dial pulses, the present invention establishes an upper and a lower detection threshold. For a valid dial pulse to be detected, the line current must drop through both thresholds, and then rise again through at least the lower threshold. With the provision of a detection delay following detection of the leading edge of a dial pulse, the presence of a valid dial pulse can be registered. The present technique used in detecting the presence of dial pulses substantially reduces the chances of rejection of a valid dial pulse which has a grossly distorted waveform.
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