ADA4937-1 drive AD9284

Hi there,

My customer is designing ADA4937-1 to drive AD9284 for his project. He follow AD9284-250EBZ schematic design, however there are some questions.

1) In EVB circuit, ADA4937-1 IN+ & IN- are swapped compared to Fig19 in AD9284 DS. Is there any impact?

2) In EVB circuit, Rf (R440 & R441) is populated. but in AD9286-500 is not populated. Is it due to the Vocm requirement difference?

3) In EVB, C418 & C419 are connected to gnd. But in AD9286-500EBZ are not. What is the reason and which one should my customer follow? 

They are using 1.2V (DC) 50ohmz termination input source. AD9284 use internal Vref and should be able to get the full span of corresponding output (0~255). Correct me if i am wrong.

Thanks and Rgds,

Keddy 

  • 0
    •  Analog Employees 
    on Jun 7, 2018 3:41 PM

    Hi,

    Let me see if I can address your questions here:

    1) In EVB circuit, ADA4937-1 IN+ & IN- are swapped compared to Fig19 in AD9284 DS. Is there any impact?

          - The difference is simply an inverting vs non-inverting configuration. Gain and performance should be the same.

    2) In EVB circuit, Rf (R440 & R441) is populated. but in AD9286-500 is not populated. Is it due to the Vocm requirement difference?

          - Actually most of the components around the amplifier should be DNI.  They are placeholders to allow for different

            configurations for the amplifier and ADC network.

    3) In EVB, C418 & C419 are connected to gnd. But in AD9286-500EBZ are not. What is the reason and which one should my customer follow?

          - This is to allow for common mode rejection if required in the configuration/application. If the SFDR is not desirable

            without the capacitors they can subsequently be added to see if an improvement can be achieved. 

     

    They are using 1.2V (DC) 50ohmz termination input source. AD9284 use internal Vref and should be able to get the full span of corresponding output (0~255). Correct me if i am wrong.

          - The ADA4937 can accept an input common mode between 0.3 and 3.0V.  The AD9284 needs an input common

             mode voltage of 1.4V. When connecting the ADA4937 to the AD9284 the VCM pin of the AD9284 should be

             connected to the VOCM pin of the ADA4937. The AD9284 is an 8 bit converter and should have a total of 256

             codes across its range.

    If you have further questions just let me know.

    Regards,

    Jonathan

  • Hi Jonathan, Thank you very much!

    My customer want to detect an analog input of 0 to 5V. I doubt this AD9284 can support. If i am correct, what will be a proper stage to implement in order to use back this ADA4937+AD9284 architecture?

    BR,

    Keddy