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ADV7393 - VBI Filtering

Question asked by CAkokhia Employee on Jan 18, 2012

I am using the ADV7393 to produce a composite video output (PAL) and appear to be seeing a reduced frequency response on certain VBI lines.

 

I generate a 10-bit digital SD video from an FPGA which includes the standard VITS17/VITS18 test signals on lines 17 and 18.  This is fed to the composite encoder and the output monitored with a VM700. 

 

I can see that the luma frequency response on the active video lines is very flat (+/- 0.2dB up to 5.8MHz), and also line 17 appears to be fine.  However, line 18 (VITS18 multiburst) is clearly being filtered and heavily attenuated at the higher frequencies.  Moving the test signal down into the active lines and the high frequencies come back again.

 

In the datasheet I can't find any reference to filters that are switched in and out for different VBI video lines.  We're not using any of the VBI generation inside the chip as we do this ourselves.

 

Can I control the filtering on Line 18?

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