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ADV7842 SD frequency sweep

Question asked by s.gremba on May 27, 2011
Latest reply on May 27, 2011 by GuenterL

I've another question about ADV7842. I've mesured the frequency response in CVBS SD PAL format. I used for that Tektronix SPG300 Video Generator (multiburst pattern). Digital video data after ADV7842 was converted to SDI format to view on Tektornix WFM7100 Video Analyser. Result looks like this:

 

sweep_adv7842.JPG

 

Last bar luma freqency is 6MHz. ADV7842 Attenuaties it about 1.3dB.

 

For comparision I've measured frequency response of ADV7181C in the same application:

sweep_adv7181C.JPG

I know that 1.3dB is not a big deal, but our client wants to use our hardware in broadcast solutions, where this is unacceptable.

I've tried to switch off every filter to extend frequency response, but that doesn't help. I've found in Hardware Manual Figure 22 (on page 115) frequency response of internal decimation filters and in fact this filterrs attenuates a little bit at 6MHz. Is it possible to change response of that filter, or we have to use older decoder like ADV7181C with separate HDMI receiver?

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