| 摘要 |
PURPOSE:To stably detect a state where the continuity of teletext signals cannot be maintained no longer, by producing a gate signal synchronously with a clock out of the clocks for processing teletext signal data and detecting the phase of the gate signal and a synchronizing signal from which a equalizing pulse is removed. CONSTITUTION:An equalizing pulse removing circuit 7 detects the period during which horizontal synchronizing signals exist from data sampling signals (clock) (fsp) and horizontal synchronizing signals (fh) containing equalizing pulses and supplies horizontal synchronizing signals from which equalizing pulses are removed to a horizontal synchronism continuity/discontinuity detecting circuit 9 by using the detecting output. The circuit 9 produces gate signals which are synchronized to the clocks from the data sampling signals (clocks) (fsp). Then the circuit 9 detects the phases of the gate signals and horizontal synchronizing signals (waveform o) from which the equalizing pulses are removed and which are supplied from the equalizing pulse removing circuit 7 and respectively outputs horizontal synchronism continuity/discontinuity detecting signals to output terminal 10 and 10'. Therefore, a state where continuity of teletext signals cannot be maintained no longer can be detected stably.
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