JPS5461505A - Drop-out detector for video image recording and reproducing appapatus - Google Patents

Abstract

PURPOSE: To reliably detect the drop-out, without inviting any mixture with the varying phenomena in a time axis, by detecting both the drop-out and the time axis variation during the reproduction so that the time axis variation is overlapped upon a reference voltage.

CONSTITUTION: The reproduced FM signals from a terminal 1 are converted into pulses by a differentiating and both wave rectifying circuit 3 so that they may be converted into video signals through a constant pulse width circuit 5 and an LPF 6. Burst signals are extracted from the video signals, and their phase is compared with the phase of the signals from a voltage control type oscillator 13 so that the error signals are partialy overlapped upon a preset voltage by means of comparison voltage generators 14 and 15. If the period of the video signals is varied with the varitation in the time axis, te comparison voltages of comparison circuits 16 and 17 are varied so that they are compared with the video signals from an integrating circuit 4. Thus, in order to eliminate the interference for the detected voltage level, which is exerted upon the detected voltage level of a drop-out by a time axid variation, the voltage level variation due to the time axis variation is overlapped upon the drop-out detecting level so that the time axid variation can be prevented from being detected as the drop-out in an erroneous manner

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