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ADV7604 Input voltages vs. ADC output values

Question asked by p_s on May 12, 2015
Latest reply on May 22, 2015 by p_s

I'm using the ADV7604 to receive VGA RGB video and I'm trying to get a better understanding of how the output values from the ADV7604 ADC relate to the voltages of the input video signal. From what I understand, there seem to be a number of factors that might affect the output values on the parallel bus of the ADV7604. I had a few questions about how the ADCs work that I was hoping someone might be able to help with:


1) What's the ADC's reference? I'm setting the REFERENCE_TRIM [2:0] register to 3'b100 as suggested in section 6.2.2 of the hardware reference manual. Does this set the ADCs internal reference to 1.4V and hence is the 12-bit ADC output split over this range? E.g. does a 0.1V input equate to an output of ((0.1/1.4) * 4096)?


2) What is the relevance of the voltages 1.2V, 0.7V and 0.5V labelled on the diagram of section 6.2.3 and how does this relate to the REFERENCE_TRIM setting of 1.4V?


3) I understand that there is a clamp on the input to ensure that the DC offset of the incoming signal does not cause clipping of the ADC. The datasheet appears to suggest this clamp is fixed at 0.89V typical. Will this cause the output from the ADV7604 to be offset as well or is the offset removed because the ADC reference is differential? If so, what are REFN and REFP set to?


4) How do the fine tuning CLMP_A/B/C and A/B/C_OFFSET registers in the CP_MAP affect the output value? Again will this apply offsets to the output of the ADC or is this more fine tuning to ensure the signal is in the correct location?


Any help on this would be greatly appreciated.


Many thanks