Contrast control wherein reference pulse detection occurs every other line period and wherein clamping occurs in remaining line periods
AssigneeSony Corporation
InventorsShunji Umemura, Hiroyuki Nakazono
Life of this patent
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Abstract
The present invention provides a contrast control circuit capable of controlling the contrast even if the back porch is comparatively short. The contrast control circuit comprises monostable multivibrators (24, 26) which provides a background pulse and a reference pulse alternately, respectively, a switch (SW1) which clamps a video signal while the background pulse is HIGH so that the potential of the pedestal level is zero on an (N+1)th horizontal scanning line, and a switch (SW2) samples the leading edge of a reference pulse inserted in the video signal while the reference pulse is HIGH on an nth horizontal scanning line.
Claims7
A contrast control circuit comprising:
- a clamping means for clamping a video signal so that the potential of the pedestal level is held zero once every N horizontal scanning cycles, where N is an integer not smaller than two;
- a voltage detecting means for detecting the reference voltage of a reference pulse inserted in a horizontal back porch, once every N horizontal scanning cycles other than the horizontal scanning cycle in which said clamping means clamps a video signal so that the potential of the pedestal level is held zero;
- and
- a control means which generates a contrast control signal on the basis of the reference voltage detected by said voltage detecting means and a specified voltage specified by operating a specified voltage setting source.
A contrast control circuit which comprises:
- means for extracting a horizontal synchronizing signal from an input video signal each horizontal scanning cycle;
- means for generating a background pulse in response to the horizontal synchronizing signal once every N horizontal scanning cycles, where N is an integer not smaller than two;
- means for generating a reference pulse in response to the horizontal synchronizing signal once every N horizontal scanning cycles signal other than the horizontal scanning cycle in which said background pulse is generated;
- means for inserting said reference pulse in a back porch of the video signal;
- means for clamping the video signal so that the potential of the pedestal level is held zero in response to said background pulse;
- means for detecting the voltage of said reference voltage inserted in said back porch;
- and
- means for generating a contrast control signal on the basis of the detected voltage and an operator specified voltage;
Dependencies are inferred from the claim text.