I use ADV7193 video encoder with ADA4430. ADA4430 output is connected to ADV7182. I generate color bar with ADV7391 and capture it with ADV7182. ADA4430 output is circutry is designed as shown in the datasheet (http://www.analog.com/media/en/technical-documentation/data-sheets/ADA4430-1.pdf ) (page 13 figure 29).
The CBVS video is connectted to the ADV7182 input. ADV7182 input ciruitry is also designed as shown in the datasheet (http://www.analog.com/media/en/technical-documentation/data-sheets/ADV7182.pdf ) (page 13 figure 6).
The white and the yellow colors cannot be captured. White and yellow are received as gray(808080 - YCbCr) . Can you help about this issue? Does the schematic causes this problem?
Increasing the 47 uF just lowers the low pass break point which will help with holding the video signal up.
SAG circuits first came out when large ceramic caps were expensive so the first designs used…
The peak-to-peak amplitude of the signal is about 800mV. The measurement in the image is taken from the input pin of ADV7182. The other colors are normal.
Check the amplitude of the analog signal going into the ADV7182. You might be chopping off the color signal on the waveform. I'm assuming other color show up normally.
Your are clipping white and yellow Chroma. Sync pulse looks too deep. I'd have to see more of the schematic to give a suggestion. Are you sure the power rails to the op-amp are good?
When I disconnect ADV7182 and only observe the output of ADA4430, I get the waveform in below.
The analog video schematic is below.
Can R45 (75ohm) causes the problem. I have just scoped the ADV7391 output, All colors are normal, There is no clipping. I think, opamp gain is too much. How can I decrease it?
I am using ADV7391 in "full drive" mode (Rset = 510ohm, RL=75 ohm). Should it be "low drive" mode (Rset = 4.12k, RL = 300ohm)?
ADV7182 side is below
I will change R45 and R40. Thank you for your advice.