Simulation Problem of ADA4938-1

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 Emman.A

     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

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, Emman.A

      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 ？