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 Initial Condition for Inductor 

Last post Mon, Jun 1 2009 9:32 PM by tester. 8 replies.
Started by tester 24 May 2009 04:28 AM. Topic has 8 replies and 5229 views
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  • Sun, May 24 2009 4:28 AM

    • tester
    • Top 150 Contributor
    • Joined on Thu, Apr 23 2009
    • Posts 45
    • Points 895
    Initial Condition for Inductor Reply

    Dear All,

    I am using  Cadence IC5141 and running a simulation which requires the ".IC" setup for inductors. I tried to put some value under the "initial condition" field of the inductor, but the value is going when I doubly confirmed it with the transient analysis. Are there anything that I may miss or the initial condition of the inductor does not work at all? By the way, are there any alternative way to figure this out? Thanks a lot in advance.

     

     

     

    • Post Points: 20
  • Tue, May 26 2009 2:52 AM

    Re: Initial Condition for Inductor Reply

    I'm not sure what you mean by "the value is going". You might want to clarify.

    Whether initial conditions on devices is controlled by the ic parameter for tran analysis, or the force parameter for dc. This defaults to all for tran, and none for dc. It needs to be dev or all for the initial condition to be used.

    By the way, you didn't specify which simulator you're using. What I'm talking about above is for spectre. The fact you're talking about ".IC" suggests to me you might be using a different simulator?

    Regards,

    Andrew.

    • Post Points: 5
  • Wed, May 27 2009 8:37 AM

    • tester
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    Re: Initial Condition for Inductor Reply

    Dear Andrew,

    Thank you very much for your reply and sorry for the confusing.

    What I really mean the value is going is the following:

    1. I set the inital current of the inductor as 1mA. Later, I run the transient simulation, and the inductor current at t=0 is zero.

     2. I did try to set "dev" and later "all" under the trans analysis, but none of them work.

    3. I am using "spectre"

    Thanks again and hope that helps.

     

    • Post Points: 20
  • Wed, May 27 2009 8:44 AM

    Re: Initial Condition for Inductor Reply

    Is this an inductor from analogLib? Or from some other library? Perhaps the other library has a field for initial condition but doesn't netlist it, or doesn't use it? I tried this myself and it does work...

    If you have a simple small testcase, can you paste the input.scs here?

    Regards,

    Andrew.

    • Post Points: 20
  • Thu, May 28 2009 10:17 PM

    • tester
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    • Joined on Thu, Apr 23 2009
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    Re: Initial Condition for Inductor Reply

    Dear Andrew,

    I am using the inductor in analogLib, and here is the input.scs testing file. Thank you again for your help.


    // Design view name: schematic
    simulator lang=spectre
    global 0

     

    // View name: schematic
    V1 (net38 0) vsource dc=1.8 type=dc
    R1 (net31 net15) resistor r=1K
    R0
    (net30 net13) resistor r=1K
    C2 (net30 net31) capacitor c=300f ic=-30m
    C1
    (net13 net15) capacitor c=100f ic=300m
    L1 (net38 net31) inductor l=70n
    L0
    (net38 net30) inductor l=70n ic=500u
    ic net13=0.35 net30=-40m

    simulatorOptions options reltol=1e-3 vabstol=1e-6 iabstol=1e-12 temp=27
    tnom=27 scalem=1.0 scale=1.0 gmin=1e-12 rforce=1 maxnotes=5 maxwarns=5
    digits=5 cols=80 pivrel=1e-3 sensfile="../psf/sens.output"
    checklimitdest=psf
    tran tran stop=0.001m errpreset=conservative
    maxstep=100p ic=all  write="spectre.ic" writefinal="spectre.fc"
    annotate=status maxiters=5
    finalTimeOP info what=oppoint where=rawfile

    modelParameter info what=models where=rawfile
    element info what=inst
    where=rawfile
    outputParameter info what=output where=rawfile
    designParamVals
    info what=parameters where=rawfile
    primitives info what=primitives
    where=rawfile
    subckts info what=subckts  where=rawfile
    saveOptions options save=allpub

    • Post Points: 20
  • Fri, May 29 2009 1:56 AM

    Re: Initial Condition for Inductor Reply

    I just tried this, and plotting L0:1 (the current through the inductor):

    inductor current

    As you can see, the current starts off at 500uA.

    Regards,

    Andrew.

    • Post Points: 20
  • Sun, May 31 2009 10:32 AM

    • tester
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    Re: Initial Condition for Inductor Reply

    Dear Andrew,

    Thank you very much for your try. With the same exact input.scs (unless you have changed the some of the analysis parameter, which I would love to know and give a try myself), the current starts off at 30.4mA. I do not know how to paste the simulation output into this post.

     

     

    Notice from spectre during IC analysis, during transient analysis `tran'.
        L0: Initial condition computed for node L0:1 is in error by 29.8501 mA (5.97001 k%).
        C2: Initial condition computed between nodes net30 and net31 is in error by 30 mV (100 %).
            Decrease `rforce' to reduce error in computed initial conditions.  However, setting rforce too small may result in convergence difficulties or in the matrix becoming singular.

     

    Thank you again for your help and have a nice weekend!

     

    • Post Points: 20
  • Mon, Jun 1 2009 7:33 AM

    Re: Initial Condition for Inductor Reply

    What version of spectre are you using ("spectre -W" should tell you this, or it also appears in the spectre log file)?

    To upload the picture, I just created myself an account on  pict.com and then did File->Save Image from ViVA (wavescan too) and saved a png file - I uploaded this to pict.com and then used the little image icon when posting to reference the image URL.

    I tried both an MMSIM71 ISR and an IC5141 ISR for spectre, and they both gave the same results I posted. I didn't cjhange anything - just ran "spectre indic.scs" (indic.scs was your netlist, which I cut and paste and fixed the line wraps):

    // Design view name: schematic
    simulator lang=spectre
    global 0
    
     
    
    // View name: schematic
    V1 (net38 0) vsource dc=1.8 type=dc
    R1 (net31 net15) resistor r=1K
    R0 (net30 net13) resistor r=1K
    C2 (net30 net31) capacitor c=300f ic=-30m
    C1 (net13 net15) capacitor c=100f ic=300m
    L1 (net38 net31) inductor l=70n
    L0 (net38 net30) inductor l=70n ic=500u
    ic net13=0.35 net30=-40m
    
    simulatorOptions options reltol=1e-3 vabstol=1e-6 iabstol=1e-12 temp=27 tnom=27 scalem=1.0 scale=1.0 gmin=1e-12 rforce=1 maxnotes=5 maxwarns=5 digits=5 cols=80 pivrel=1e-3 sensfile="../psf/sens.output" checklimitdest=psf
    tran tran stop=0.001m errpreset=conservative maxstep=100p ic=all  write="spectre.ic" writefinal="spectre.fc" annotate=status maxiters=5
    finalTimeOP info what=oppoint where=rawfile
    
    modelParameter info what=models where=rawfile
    element info what=inst where=rawfile
    outputParameter info what=output where=rawfile
    designParamVals info what=parameters where=rawfile
    primitives info what=primitives where=rawfile
    subckts info what=subckts  where=rawfile
    
    

     

    Regards,

    Andrew.

    • Post Points: 20
  • Mon, Jun 1 2009 9:32 PM

    • tester
    • Top 150 Contributor
    • Joined on Thu, Apr 23 2009
    • Posts 45
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    Re: Initial Condition for Inductor Reply

    Dear Andrew,

    Thank you again for your help. After running "spectre -W", I got

    sub-version 6.2.1.170

    After running "spectre -V', I got

    @(#)$CDS: spectre version 6.2.1 32bit 02/10/2008 06:20 (usim440-30) $

    Hope that helps.

    • Post Points: 5
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Started by tester at 24 May 2009 04:28 AM. Topic has 8 replies.