ADV7202: Operation of clamping function

Q

1) How does the device decide what level (digital value) to set the blank value
to initially?

2) At the moment I am reading the digital value corresponding to blank out of
the device, then I am programming the clamp register with the value derived
from this to make the gain equation correct. I am also providing a sync pulse
during blank to activate the clamp at the right point. Is this procedure
correct?

A

1. We expect the ASIC to monitor the output digital code and determine from it
where the actual blank and sync levels are. The user will then control the
clamps to 'steer' the blank level to a specific code. Note the programmable
blank level within the decoder is only a level which will not be affected by
gain or AGC. I would expect that the programmed value here will equate to the
output blank level that the customer has chosen.

2. Your method of control seems correct to me. It is important that it is AC
coupled to the part. Our evaluation board used a DC voltage clamp at its input
as we did not dynamically control the clamps. This should be removed.

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