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  1. #1
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    ltspice Time Step too small

    Hi All,

    I am getting a "Time step too small; initial timepoint: trouble with node x"

    My SPICE file is as follows:

    Code:
    MemristorHPTest
    
    ********************************
    * MemristorHP
    .SUBCKT MemristorHP plus minus PARAMS:
    + phio=0.95 Lm=0.0998 w1=0.1261 foff=3.5e-6 ioff=115e-6 aoff=1.2 fon=40e-6 ion=8.9e-6 aon=1.8 b=500e-6 wc=107e-3 
    G1      plus      internal value={sgn(V(x))*(1/V(dw))^2*0.0617*(V(phiI)*exp(-V(B)*V(sr))-(V(phiI)+abs(V(x)))*exp(-V(B)*V(sr2)))} 
    Esr     sr        0 value={sqrt(V(phiI))} 
    Esr2    sr2       0 value={sqrt(V(phiI)+abs(V(x)))} 
    Rs      internal  minus 215 
    Eg      x         0 value={V(plus)-V(internal)} 
    Elamda  Lmda      0 value={Lm/V(w)} 
    Ew2     w2        0 value={w1+V(w)-(0.9183/(2.85+4*V(Lmda)-2*abs(V(x))))} 
    EDw     dw        0 value={V(w2)-w1} 
    EB      B         0 value={10.246*V(dw)} 
    ER      R         0 value={(V(w2)/w1)*(V(w)-w1)/(V(w)-V(w2))} 
    EphiI   phiI      0 value={phio-abs(V(x))*((w1+V(w2))/(2*V(w)))-1.15*V(Lmda)*V(w)*log(V(R))/V(dw)} 
    C1      w         0 1e-9 IC=1.2 
    R       w         0 1e8MEG 
    Ec      c         0 value={abs(V(internal)-V(minus))/215} 
    Emon1   mon1      0 value={((V(w)-aoff)/wc)-(V(c)/b)} 
    Emon2   mon2      0 value={(aon-V(w))/wc-(V(c)/b)} 
    Goff    0         w value={foff*sinh(stp(V(x))*V(c)/ioff)*exp(-exp(V(mon1))-V(w)/wc)} 
    Gon     w         0 value={fon*sinh(stp(-V(x))*V(c)/ion)*exp(-exp(V(mon2))-V(w)/wc)}
    .ENDS MemristorHP
    ********************************
    Vtest test GND DC 0 SIN(0 1.8V 1 0 0 0)
    
    R0    test X 1k
    Xmemristor    X GND MemristorHP
    
    .TRAN  1m 1 uic
    
    .END

    •   Alt9th November 2011, 03:30

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  2. #2
    Junior Member level 2
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    Re: ltspice Time Step too small

    Try to decrease the step ceiling. Note that your command
    .TRAN 1m 1 uic
    is not optimal: the first number 1m has no effect to the simulation run; you have not set the step ceiling, thus it is defined automatically as 1/50=20ms and it is too high.
    Try the following:
    .TRAN 0 1 0 1m uic
    Then it works in PSpice.
    I do not work with LtSpice, thus I do not know if GND can be used for the ground. In PSpice, I replaced it by 0 (zero) in your code. Then it works fine.
    Hope it helps you.
    D.



    •   Alt9th November 2011, 19:11

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  3. #3
    Super Moderator
    Points: 21,452, Level: 35

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    Re: ltspice Time Step too small

    You might look at whether this memristor model is singular
    at any point. That's a good way to fail numerically.



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