Video signals clamping circuit for maintaining DC level of video signals
AssigneeMitsubishi Denki Kabushiki Kaisha
InventorsHideki Kaneko, Sadayuki Inoue, Ikuo Ookuma
Life of this patent
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Abstract
A video signal clamping circuit capable of maintaining a DC level of a digital video signal at a fixed level, in which a pedestal level in a vertical blanking period of the digital video signal after an A/D conversion is sampled, and an average value of a plurality of sampling data in a plurality of fields is calculated by an average value calculator. The average value is compared with a predetermined clamp level reference value by a comparison output circuit, and depending on the comparison result, a signal either added or subtracted by a certain width to or from an output signal of a predetermined period before is output for automatically controlling a clamp voltage.
Claims11
A video signal clamping circuit for maintaining a DC level of a digital video signal at a fixed level, comprising:
- an A/D converter for converting an input analog video signal into the digital video signal;
- a first latch circuit for sampling a predetermined part of the digital video signal at a predetermined period and latching the sampled data;
- an average value calculator circuit for taking in a predetermined number of the sampled data items latched by the first latch circuit and calculating an average value of the sampled data;
- a comparison output circuit for comparing the average value obtained in the average value calculator circuit with a reference value and outputting data either added or subtracted by a predetermined width to or from an output signal of a predetermined period before depending on a comparison result;
- a D/A converter for converting the data output by the comparison output circuit into an analog signal;
- and
- a clamp voltage supply means for supplying a clamp voltage to the input analog video signal on the basis of the analog signal output by the D/A converter, wherein the clamp voltage supply means includes a level compression shift for carrying out a level compression so that a voltage variation amount of the output of the D/A converter corresponding to 1 LSB of change of the input of the D/A converter is less than a voltage variation amount of 1 LSB change of the output of the A/D converter, and for shifting the voltage level to a predetermined level.
Dependencies are inferred from the claim text.