Spectre problem modelling ideal capacitor and current source

Discussion in 'Cadence' started by Maz, Jul 17, 2006.

  1. Maz

    Maz Guest

    I am trying to model a very basic system however it is not performing
    as I expected. I basically have an ideal current source (1 pA) feeding
    into an ideal capacitor model (1uF) in Spectre. I am expecting a
    linear relationship of voltage vs time based on integrating the
    capacitor current equation:

    Ic = c*(dVc/dt)

    integrating to get

    Vc = (1/c)*Ic*t = Kt, where K = (1/c)*Ic

    However, I am finding that when I attempt to model this in Cadence
    using Spectre, the simulation saturates follows an exponential
    relationship that saturates at the constant K value (1mV). I cannot
    seem to explain why it does not follow a linear function. Does the
    specre ideal capacitor model include resistance? If so, is there a way
    to remove that?

    Any help would be appreciated. Thank you.
     
    Maz, Jul 17, 2006
    #1
  2. Sorry for the very late reply. I expect you're seeing the effects of the 1Tohm
    gmin resistor added to aid convergence, since there would be no path
    to ground during DC from the current source.

    Regards,

    Andrew.
     
    Andrew Beckett, Aug 16, 2006
    #2
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