Defect detection and compensation apparatus for use in an FM sig

Details Defect detection and compensation apparatus for use in an FM sig Defect detection and compensation apparatus for use in an FM sig

1975-07-09

1977-01-04

Cardillo, Jr., Raymond F.

Facsimile and static presentation processing

Facsimile

Specific signal processing circuitry

360 38, 358128, H04N 576, G11B 906

Patent

active

040014967

ABSTRACT:
In playback of a video record (e.g., in video disc form) employing a FM carrier recording format, a defect compensation system is provided which substitutes delayed video signals for current video signals when a defect is encountered. The current video signals are obtained from the output of the player's pickup-responsive FM detector (illustratively of the zero-crossing detector type) via appropriate frequency responsive circuitry comprising a low pass filter (encompassing the recorded video signal bandwidth: e.g., 0-3 MHz.). To detect the occurrence of a defect, the FM detector output is also supplied to additional frequency responsive circuitry having a wideband response which desirably extends from DC to an upper frequency limit (e.g., 0-6 MHz.) well above the highest frequency of the video signal subject to recording. The wideband circuit output is supplied to pair of voltage level comparators, one supplying an output pulse of a given polarity whenever the wideband circuit output voltage level exceeds a level representative of the FM detector output for the maximum frequency of the FM carrier deviation range employed in recording, and the other supplying an output pulse of the given polarity whenever the wideband circuit output voltage level falls below a level representative of the FM detector output for the deviation range's minimum frequency. The comparator outputs are added together to form a defect indication signal. Switching between current and delayed video signals is controlled in response to the defect indication signal. Operation in the delayed signal mode is maintained for a short period after defect indication pulse termination (to allow video circuitry stabilization following the defect transient) by rendering a retriggerable one-shot responsive to the defect indication signal, and combining the output of the one-shot with the defect indication signal to form the switching control signal.

REFERENCES:
patent: 3865981 (1975-02-01), Welch
patent: 3912858 (1975-10-01), Kenney
patent: 3925811 (1975-12-01), Kenney
Signal Processing in the Philips `VLP` System, Van den Bussche et al., Philips Tech. Rev. 33, No. 7, pp. 181-185, 10/73.

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