Composite Video Signal (CVS) - Blanking Pulse

Make sure you read the CVS in the order given below. Links to different CVS is given at end of this explanation.

There are 4 types of CVS viz.:

1. CVS for pedestal height

2. CVS for blanking pulses

3. CVS for horizontal sync detail

4. CVS for vertical sync detail

If in exam, a question comes as ‘Explain CVS’ then depending on the marks, explain anyone that you want to explain. For 5 marks, write any from first three. I’d prefer first one as it’s easy whereas if the question is for 10 marks, go for the 4th one. The one that I've explained below is the second one.

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Apart from picture elements, a CVS also contains blanking pulses. These pulses are used to make the retrace lines invisible. Retrace is nothing but the period when the horizontal scanning beam goes back to the left side of the raster (frame) and the vertical scanning goes to the top.

The adding of blanking pulse is done by increasing the video signal’s amplitude slightly above the peak black level. This means that they are added in blank level. Whenever a retrace is done, black spots are produced on screen. The blanking pulses are added at blank level so that no spots are observed on screen as blank level is darker than black level.

CVS contains horizontal as well as vertical blanking pulse to make the respective retrace invisible. The repetition rate for horizontal blank pulse, that is the period after which the next blank pulse will occur, is same as that of horizontal frequency that is 15625 Hz and the time period (T_P) = 12 µ sec. Similarly, the repetition rate for vertical blank pulse is same as that of vertical scanning frequency that is 50 Hz and the time period (T_P) = 160 µ sec.

To elaborate the answer, you'll can add the description of Peak White level, black level, blank level, etc.

To get CVS - Pedestal height, Click Here

To get CVS - Horizontal sync detail, Click Here

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