Locked groove detection and correction in video disc playback ap

Details Locked groove detection and correction in video disc playback ap Locked groove detection and correction in video disc playback ap

1974-11-12

1976-06-15

Konick, Bernard

Telegraphy

Systems

Simplex-reversing periodic

178 66A, 1791004D, G11B 328, H04N 576

Patent

active

039638600

ABSTRACT:
When a "locked groove" condition is encountered in the playback of a video disc having sync signal recording locations non-radially aligned in successive groove convolutions, each initiation of a repeat reading of the same groove convolution(s) results in a timing disturbance of recovered sync signals. The disturbance is detected by an arrangement employing a phase locked loop responsive to the horizontal sync component of the recorded signal. A filtered error voltage output of the phase locked loop is applied to a voltage comparator to effect discrimination against noise and minor, transitory timing disturbances. A staircase voltage generator, responsive to the voltage comparator output, provides an output sufficient to trigger generation of a locked groove recognition pulse, when the voltage comparator threshold is exceeded a sufficient number of times within a selected time period to verify locked groove behavior and continuance. To avoid false generation of a locked groove recognition pulse under certain transient conditions (such as stylus set-down, stylus jump due to player jarring, et al.), a retriggerable one-shot is interposed between the voltage comparator and the staircase voltage generator, and provided with parameters aiding discrimination against the relatively high frequency of the repetitions of sync timing disturbances that are associated with such transient conditions. A suitable locked groove escape mechanism (e,g., a piezoelectric groove skipper element, effecting radial motion of the stylus) is activated to advance the stylus forward in its radial travel upon generaion of a locked groove recognition pulse.

REFERENCES:
patent: 2921992 (1960-01-01), Bick
patent: 3437763 (1969-04-01), Anderson
patent: 3706861 (1972-12-01), Giel
patent: 3711641 (1973-01-01), Palmer
patent: 3715524 (1973-02-01), Adler
patent: 3787616 (1974-01-01), Falk

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