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Simulation Problem of ADA4938-1

Dear Emman.A,

         I want to use ada4938-1 to drive the ADC ad9629, before we start the design,  I do the simulation of ada4938-1, but I met some problems when I do the simulation. 

software: Orcad PSpice

the steps of simulation:

    First , I get the ada4938.cir on the website, and generate the ADA4938.lib and ADA4938.OLB by Module Editor

    Second , draw the schematic:

         1)the schematic used the THEORY OF OPENRATION in ADA4938 datasheet.  Input = 2Vpp,10MHz sine wave,  gain 1V/V ,output should be 2Vpp

 

Then start the simulate, but simulation stop and appear follows

So, I change the setting to 0.1 in the red rectangle,and get result,but the result is not consistent to theory. I guess the bad result is related to the setting

So is there the mistake in the steps of simulation or in the schematic?  I hope you can give me some suggestion or right steps.

 

Thanks for your kind consideration and looking  for your early reply.

Top Replies

  • Hi,

          Firstly,Thanks for your kind reply.

          I have tried your advice in my SPICE simulation, but I didn't slove the problem, so I used the software ADIsimPE which you recommended. I did my simulation…

  • Hi 仕政 朱,

    It seems to me that the connections of R4 and R7 to the output voltage was interchanged. Can you confirm? Please see attached picture below. Try to connect R4 to node 71(pin8) and R7 to node 71B(pin7) instead. Let see of this gonna solve your problem. If this doesn't work, can you attached your simulation file here so that I could play around with it and check where the trouble is coming from.

    Best regards,

    Emman

  • HI 

         I have tried to connect R4 to node 71(pin8) and R7 to node 71B(pin7) instead, but the simulation result didn't change. So I have attached my simulation file here, and hope you can check where is the trouble coming from. Thank you !

     

    Best regards,

    Shizheng Zhu

    testad4938_1-PSpiceFiles.rar
  • Hi 仕政 朱 ,

    My PSPICE simulation is down today and therefore I was not able to open your file.

    Another obvious mistakes that I noticed on your schematic is that your negative supply voltage (Node 50; Pin 6) should be connected to -5V and not on the ground. Your input voltage is +/- 2V and therefore it should be between your supply rails so that you will not violate the input voltage range of the amplifier. I hope this will solve your issue.

    As for my simulation, I used the Simetrix since most of our recent updated amplifiers are available on this platform. You can get it for free on our site on this link: http://www.analog.com/en/design-center/interactive-design-tools/adisimpe.html

    It has a better symbols and almost all the model that we released are available on that platform.

    Best regards,

    Emman

  • Good to hear that you have now a working simulation. For your questions about determining your supply voltage, it is important to always refer on the datasheet. The parameter that you need to check for this kind of amplifier is the Input common-mode voltage as well as the VOCM as shown below.

    You can tie up the negative supply to ground as long as you have enough VOCM.

    I strongly recommend to download the ADIdiffcalc on our web. This will help you finalizing your design. You can do different configurations and it will tell you if your circuit will work or not. It also shows calculations of expected performance.

    Here is the link: http://www.analog.com/en/design-center/interactive-design-tools/adi-diffampcalc.html

    Here is the configuration that I imagine base on our conversation.

    Just let me know if you need further assistance. We are happy to help.

    Best regards,

    Emman

  • Hi,

          Firstly,Thanks for your kind reply.

          I have tried your advice in my SPICE simulation, but I didn't slove the problem, so I used the software ADIsimPE which you recommended. I did my simulation, and  got the result same as the theory.

    But I have a question :  Is the negative supply must be connected to -5V ?

    For example, if my input voltage range in 0.5V ~1.3V, can I connect the negative supply to the ground ?