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simple RC circuit

Sali

 Dear all,

Can some one help me to understand why the voltage at time zero drops to a value less than 1 V?

Please check the attached file.

Thanks, 

Parents

  • I've run it through spectre, getting your results. If you think something is strange read your simulation logs:

      Notice from spectre during IC analysis, during transient analysis `tran'.
        C0: Initial condition computed for node net04 is in error by 909.091 mV.
            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.

     Now in your options rforce is set to "1", which is forcing a 1Ohm resistor over the cap to find a DC solution.
    Reduce that rforce to smalller values. You still will get some error in the initial condition but not by that magnitude.

    What are you trying to simulate? Would be a better idea to have a settled system before hitting it with the pulse.

     

    Marc

     

Reply

  • I've run it through spectre, getting your results. If you think something is strange read your simulation logs:

      Notice from spectre during IC analysis, during transient analysis `tran'.
        C0: Initial condition computed for node net04 is in error by 909.091 mV.
            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.

     Now in your options rforce is set to "1", which is forcing a 1Ohm resistor over the cap to find a DC solution.
    Reduce that rforce to smalller values. You still will get some error in the initial condition but not by that magnitude.

    What are you trying to simulate? Would be a better idea to have a settled system before hitting it with the pulse.

     

    Marc

     

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