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AD725 RGB to NTSC YTRAP filter artifacts on the video output

Question asked by raztiko on Jan 31, 2014
Latest reply on Feb 6, 2014 by jpearson

Hi

 

I'm using the AD725 as RGB to NTSC converter (composite video output).

 

I use an RGB input signal from a RGB generator that has several distanced vertical lines.

 

The Composite output has a shadow on every vertical line because of the YTRAP filter.

 

I use the recommended values for C, L from the datasheet and I get this shadow (because of the filter)

 

When I increase the Q factor of the filter (narrow filter) I get color artifacts on the output signal (The YTRAP filter is hardly helping to remove the chrominance) .

 

When I decrease the Q factor of the filter (wide filter) I get more shadow.

 

You can see the attached filters that I used 3 type of filters. the input is the green signal on the bottom (variable frequency over one line). the output is the composite signal that if filtered.

 

Every file name has a the values of L, C.

 

I also used an RGB generator that inputs a text to the converter and got shadowed text.

 

I can not use the YC output. I must use composite output.

 

How can I improve the sharpness of the output signal without having colors artifacts on the output?

 

Is it a limit of the converter or is it a correct response to a vertical single line?

Best regrads,

Raz

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