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Ultrasim simulator Problem

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I built a simple resistive ladder for voltage divider circut with componenets in analogLib. When I tried to simulate this circuit with Ultrasim simulator, the intermediate nodes failed to show the output waveform excepting ground and supply nodes. I added them in the outputs list,tried save all method but none of them worked. It happened with both SPICE and Spetre netlisting formats. I tried this simple circuit when a complex circuit failed to simulate properly. Hence now I find that the resistor is not identified properly in the Ultrasim simulation. Is there any known solution for this probelm??

Thanks in advance for your suggestions


Originally posted in cdnusers.org by gunturikishore28
Parents


  • I think the core issue is centered around the following statement:

    subckt rnwell (n2 n1)

    parameters l w lr=l wr=w rsh=rnwell dl=1e-6 dw=-1e-6 vc1=1e-2 vc2=1e-4 tp=temp
    rnw (n2 n1) resistor r= " mathematical expression which evaluates fine with spectre simulator"
    end section res

    previously The model was bsource with spectre which is not identified with ultrasim simulator. I changed the model now to resistor which is identified but not working properly.

    The vc1 and vc2 are probably voltage coefficients, sounds like you were modeling a voltage controlled resistor (i.e. one in which the resistance changes as a function of the voltage across it).
    To do this right, you need to use a bsource or AHDL component of some form...the standard "resistor" component which you are using for rnw in the rnwell subckt doesn't support these kinds of expressions.

    My bet...it all worked fine in Spectre with the bsource. Ultrasim doesn't support the bsource so you switched to a resistor instead. But the resistor won't understand the voltage controlled expression you give it...and so it probably evaluates to r=0 or something...which Ultrasim then optimizes out as a short and so your resistor disappears.

    D


    Originally posted in cdnusers.org by donshreds
Reply


  • I think the core issue is centered around the following statement:

    subckt rnwell (n2 n1)

    parameters l w lr=l wr=w rsh=rnwell dl=1e-6 dw=-1e-6 vc1=1e-2 vc2=1e-4 tp=temp
    rnw (n2 n1) resistor r= " mathematical expression which evaluates fine with spectre simulator"
    end section res

    previously The model was bsource with spectre which is not identified with ultrasim simulator. I changed the model now to resistor which is identified but not working properly.

    The vc1 and vc2 are probably voltage coefficients, sounds like you were modeling a voltage controlled resistor (i.e. one in which the resistance changes as a function of the voltage across it).
    To do this right, you need to use a bsource or AHDL component of some form...the standard "resistor" component which you are using for rnw in the rnwell subckt doesn't support these kinds of expressions.

    My bet...it all worked fine in Spectre with the bsource. Ultrasim doesn't support the bsource so you switched to a resistor instead. But the resistor won't understand the voltage controlled expression you give it...and so it probably evaluates to r=0 or something...which Ultrasim then optimizes out as a short and so your resistor disappears.

    D


    Originally posted in cdnusers.org by donshreds
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