Smearing problem when use ADA4858-3 driving and equalizing a 100M VGA cable

Dear Sir,
I am working on ADA4858-3 and I am facing some technical issue.

I designed Amplifier Driver using ADA4858-3 driving and equalizing a 100M VGA Cable ,based the application note written by an ADI application engineer via below link. Please check the attached schematic for my design.

http://www.analog.com/library/analogdialogue/archives/44-07/vga_driver.html

I have serious smearing problem in the VGA output image even worse than the situation without  this ADA4858-3 driver circuit.

Would you please help to check and give some professional advice?

attachments.zip
  • hi,

    will look into this. ill update you soon.

    thanks,

    ahbie

  • hi, Jane.

    I simulated a part of your circuit and it turns out that your magnitude vs. frequency is way far compared to the figure 5 of your reference. I've noticed that the value of your RG is 56ohm compared to the 15ohm on the app note.

    the magnitude level was improved when i tried to change R109 (56R) to 15R, and for the load, try to remove R127 (75R) and R116(150R).

    Attached in this thread is the simulation i made based from your circuit. Kindly check if I put the right components in the circuit simulation. Try tweaking some components and see improvements.

    regards,

    ahbie

  • Hi Ahbie,

    Many thank for your reply.

    We will have a try to change R109 (56R) to 15R at first.

    What's more, In the previous exisiting actual circuit, R116 was NC, and the ADA4656-3 R/G/B output were connected directly to a video processor behind (do not via a cable),  maybe the series resister R127/ R160 / R156 75ohm could not be removed.

    regards,

  • 0
    •  Analog Employees 
    on Aug 2, 2018 2:38 PM
    This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

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