composite blanking extraction from video

composite blanking

Hi,

I want to extract composite blanking from video.

I have used voltage comparator for this purpose but it does not give stable waveform.

Is there any other method to extarct composite blanking from a composite video signal?

You can use the BACK PORCH output from the LM1881 Video Sync Separator IC ..
There are several manufacturers of this IC so seach for the number - letters may be different ..
eg. GS1881, the same thing ..

rgds,
IanP

LM1881 generates composite sync, vertical sync, odd/even and back porch sinals. The back porch is very different from composite blanking signal. How can we use back porch instead of composite blanking?

Hey qasmi,

Being old and wizened, and once of the 625 line fraternity, I seem to recall the expression 'blanking' is merely a term applied to the VBI 'vertical blanking interval' - exclusively. The word 'blanking' conveys that there was no active video signal present, ie it must sit at black for this period; it was required to allow the CRT scan coils time to whip the beam back up to the top again !

As the World moved on from steam powered valves, and the control of scanning improved for all sorts of reasons, the need for all that blackness in the area of the vertical interval was unnecessary.

As it seemed a waste of resource these lines led to and were used (at least in the 626 line World) for data (teletext) and test signals VBI line 19, 21, (test 2T pulse&Bar etc). And in the studios on video tape for VITC (Vertical Interval Time-code).

The LM1881 extracts it all, there ain't any more.

Happy Holidays !

2Old.