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ADV7393 roll off on VITS line 18 of VBI

Question asked by Zippy on Apr 21, 2015
Latest reply on May 13, 2015 by PaulS

Hi,

 

We are using an ADV7393 in SD slave timing mode 0 (embedded SAV/EAV). We are generating the VITS (Vertical Interval Test Signal) and inserting these into the VBI lines 17, 18, 330 & 331. But we are having issues with the CVBS output of line 18. There appears to be a -3dB roll off starting at about 4.5MHz which destroys the test signal. The following screen shot shows lines 17 and 18

 

ADV7393 - Reg 8A - 0x8.BMP

 

Our HSYNC and VSYNC lines are tied to VDDIO I expected no other SD timing mode to work. But if I now enable timing mode 1 or mode 3 then I see the following

 

ADV7393 - Reg 8A - 0x9.BMP

 

Which is the expected waveform for line 18.

 

So I now know the ADV7393 has the ability to pass though VBI data unmolested so the question is how can I achieve this same effect when only using timing mode 0?

 

Cheers,

Richard

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