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Query regarding ADV7441A -- Analog video input

Question asked by ashvin.dedakiya on Apr 4, 2011
Latest reply on Apr 14, 2011 by ashvin.dedakiya

Hello,

 

We do have query for front end voltage divider on analog video input lines for ADV7441 Video decoder as below,

- Refer to ADV7441_HW_RevJ manual, section 3.1, page-22,

        o   Recommended Resistor Divider Network (24/51 ohm) for 1.6 V Range Video Signal and  Recommended Resistor Divider Network (36/39 ohm) for 2 V Range Video Signal

        o   What should we do if want to support different type of video source in same system (Source-A having 1V range video signal, source-B having 1.6V range video signals and Source-C having 2V video signal)?

 

Observations:

We have used 24/51 ohm resistor voltage divider in our circuit (as used in "ADV7441A Typical Connection Diagram"). Below are observation with this,

1. Video source = Sony Camera (720p), video detected but not in sync (see attached waveforms and snap with 01_xx)

2. Video source = DVD player (720p), video detected but not in sync (see attached waveforms with 02_xx)

 

We replaced votage divider resistors to termination resistors with 0/75 ohm. Below are observation with this,

3. Video source = Sony Camera (720p), video detected (in sync) with BAD colors (see attached waveforms and snap with 03_xx)

 

As per my understanding typically video signals are of 1V peak to peak, so not able to understand use of voltage divider here.

Please suggest.

 

Thanks & Regards,

Ashvin Dedakiya

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