| 摘要 |
This lock-off alarm circuit is associated with a phase-locked loop 10 including a phase comparator 14 receiving on an input 11 a reference signal R consisting of pulses which repeat at a frequency with which the loop is to be synchronised and on another input a measurement signal consisting of a rectangular clock signal H. It includes means for fixed delay 21 generating versions R', H' of the reference signal and of the measurement signal in which the pulses of the reference signal are centred, when the loop is locked on, in the middle of the first half-periods of the rectangular measurement signal, sampling means 22 sampling the version H' of the rectangular measurement signal delivered by the means of fixed delay 21 at the instants of appearance of the pulses of the version R' of the reference signal, which version was delivered by the means of fixed delay 21, integration means 23 operating on the samples delivered by the sampling means 22 and threshold-comparison means 24 operating on the level delivered by the integration means 23 and providing in response a lock-off alarm signal. <IMAGE>
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