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AD7626 circuit not working above 1 MSps

Question asked by atrajesh on Jul 2, 2015
Latest reply on Jul 3, 2015 by jcolao

Hi,

 

 

I designed a board using Altera CycloneIV GX FPGA and AD7626. I followed CN0105. I maintained separate power planes, and also followed the recommendations for AGND/DGND. The ADC was working beautifully for sampling rates upto 1 MHz. But above this rate, I am observing horrible behavior. I have followed the timing requirements carefully. Unfortunately I don't have any signal integrity tool here. Nor do I have the ADC evaluation software or test-jig.

 

 

I feel that the problem lies in the sampling clock coming from the digital domain. The clock is driven by the FPGA. For 1 MSps rate, the sampling clock is 20 MHz. I feel that at this rate, analog domain is not getting polluted. But if I have to sample at 10 MSps, I need to drive the sampling clock at 200 MHz. I think this is creating havoc in the analog domain.

 

 

The main issue is that the ADC has serial output. So the converted data needs to be driven out at a high rate. Is it recommended that parallel output ADCs be used for higher sampling rates.

 

 

Any thoughts/feedbacks will be highly appreciated.

 

 

regards,

 

rajesh

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