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OpAmp Simulation in Cadence Spectre

Shahnaf
Hi, I have used OpAmp symbol from Solutions library (default library of cadence). As an initial step, I have simulated a basic circuit in Op Amp. But I am not getting the desired output. Moreover, I have checked the cadence simulation manual for Op Amp. I found something difference in the symbol (from Solutions library) to that of the Cadence manual. Can you please let me know where I am wrong and what needs to be corrected? Thanks, Shahnaz
  • Ya....Andrew, I understand your situation. I found op_amp schematic in Solutions library with differential amplifier and CS amplifier as blocks. Then I got to see the schematic of the differential amplifier and CS amplifier in the "Solutions" folder. Screenshot.png and screenshot-6.png shows the Solutions library. Screenshot-1,2,3,4 are the block diagram of the OpAmp and its internal schematic. Screenshot-5 is the OpAmp which I simulated Snapshot.png is the plot I got. I have attached the circuit I have used. My intention is to use OpAmp as linear multiplier for ASK modulation. But I had never used Opamp in my design. Moreover, I had never used any symbols from "Solutions" library. In order to test whether the symbol suits to my application, I had simulated a simple voltage amplifier circuit which amplifies the input signal by 10 times. The last two are the sample circuit I simulated and the plot I got. But the expected plot is 10 times the input signal. I am out of office and so couldn't check the path. Just see whether you can provide any hint based on the attached files. Thanks in advance.
    refwrfdesignforumopampsimulationincadencespectr.zip

  • Looking at your picture (Screenshot-5.png), you have a sine wave input with 5 volts amplitude. With a gain of 10, you'd have 50V output amplitude, but you only have +/-15V supplies, so clearly it wouldn't be able to generate signals that big. That's one mistake, at least (although don't think it's the only one).

    The Solutions library appears to be in the cadence_ms_labs_613 directory - you probably should try to find out where that came from. Is +/- 15V even suitable supply voltages? That's not exactly typical for modern processes...

    Going into the detail of why this circuit (for which I can't see any more than just some screenshots) is not really something I have time to do; maybe somebody else can spare the time - but the right things to  do are probably either to read a book on analog circuit design, or to contact whoever provided this "lab" database and find out how it is intended to be used, or to look at other configurations in the same library and try similar situations. It's an artificial example anyway, so it's not going to help you unless it's realised for a specific process which is the same as the process you're planning to use.

    Regards,

    Andrew.

  • I want to do differential amplifier design and simulation results of  differential ampifier in 180nm technology using cadence virtuoso .So, please help me to simulate on AC analysis.

     

  • Please read the forum guidelines. You didn't really ask a question, at least not a precise question. Also, you posted on the end of a 2 year old thread, which the guidelines ask you not to do.

    Andrew.

  • Andrew Beckett said:

    Please read the forum guidelines. You didn't really ask a question, at least not a precise question. Also, you posted on the end of a 2 year old thread, which the guidelines ask you not to do.

    Andrew.

     

     

  • i want to design a differential amplifier in cadens , but i m confuse from were to start ? 

  • At the beginning? If you're confused, then I'm confused as to why you quoted a post I'd made in this thread asking somebody not to post on the end of a 2 year old thread with a vague question and then you proceed to do precisely that! In fact you didn't really even ask a question - it was a statement with a question mark at the end...

    I suggest you start a new thread with a question which clearly explains what you are trying to do, what you have tried, what you've read - otherwise nobody knows what your actual issue is. It is so open ended - we have no idea quite how far back your confusion is. Do you:

    • Not know how to find the building with the computer in?
    • Not know how to turn the computer on?
    • Not know how to log in?
    • Not know how to start virtuoso?
    • Not know where to find a book or papers explaining the principles of amplifier design?
    • Not know where the PDK is?
    • Not know how to use the schematic editor?
    • Not know how to run ADE?
    • Not understand what any of the analyses do?
    • Not know what the metrics you need to test against?
    • Not know how to make those measurements in ADE? 

    I could go on (and maybe I'm being harsh here) - but if you don't follow the forum guidelines and ask a well framed question, you'll either get a vague answer or (quite likely in this case) no answer at all because you can't realistically expect somebody to explain differential amplifier design in Virtuoso (I don't know what "cadens" is) without knowing where you are starting from.

    Maybe you should just speak to your supervisor.

    Regards,

    Andrew.

  •  Hi

    I have a question

    I want a opamp that i select its parameters for example gain= 60dB and input common mode is zero.

    please help me.

    I cant find opamp in my library .

    best regards,

    Fatemeh

  • Hi Andrew,

    I would like to model an ideal integrator in Cadence. Currently, I am using "VCVS" as an amplifier shown in the attachment.

    When I simulate the circuit, apparently, capacitive-feedback does not work properly, however, I have added a large resitor in series with the capacitor. The opamp model acts like a comparator, i.e. As long as negative input has a larger voltage than the positive input, output shows the minimum voltage and Vice versa. I am wondering if you might how to resolve the issue!

    Do you have any suggestion how to model an ideal integrator in Cadence? Preferably, I do not want to use Verilog-A opamp. 

    Thanks.

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