We found the input DC level fluctuated in about 2mV with CVBS input.
Is there any way to improve it?
We observed it was iimproved a little bit when the bias current was reduced.
Is there any side effects with it?
1) Can you identify any specific frequency with this 2mV bouncing? For example if it was 60Hz it might point to a power supply issue (isolation)
2) Yes it could be a layout or grounding issue
3) If reduced current helps and it doesn't effect any other functionality then you can change it. We just don't have a lot of experience past the recommended setting, however the register is documented so it is something you can experiment with.
Can we get some more information on this?
1) Where are you measuring the DC level at on the schematic. The CVBS input is AC coupled
2) Which bias are you changing??
1) Yes,The CVBS input is AC coupled.
We observed the offset level or should I say black level.
We observed SDI signal by using digital wave monitor after A/D conversion.
Please refer to the attached file.
The amplitude stays in 700mVpp but it looks like the whole waveform goes up and down about 2mV.
2) We changed the register 0x3B,(Bias Control).
The default is 600uA but reducing it improves the above phenomena.
What the root cause of the fluctuation could be?
Is there any possibility of layout issue like large inductance and resistance of GND line?
Is it OK to reduce the bias current?
If ADI had no idea please let me know.
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