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[Virtuoso] What is wrong with my RC transient simulation ?

Leey

Hi,

   I am trying to do a simple RC transient simulation in Cadence virtuoso. Please see the circuit below:

I am trying to see the transient current and voltage of the capacitor being charged,however I got the following simulation result:

where /net3 is the capacitor voltage and CO/plus is the capacitor current. This looks totally incorrect, and I have my simulation configuration as:

Could anyone help me figure out the issue? Thanks!

  • Leey

    Sorry, something wrong with my uploading, here is the simulation result:

  • sjwprc
    in reply to Leey

    Hi, you give DC source with cap as load, so the circuit is open. No current. 

  • Leey
    in reply to sjwprc

    Thanks Sjwprc, but my goal is to see the transient current and voltage waveform when a cap is being charged. That is why I am using DC source for a cap.  

  • Andrew Beckett
    in reply to Leey

    You won't see any transient current or voltage as the capacitor is charged if you use a DC source. The DC operating point will find (in effect) the settled DC steady state. This is done by leaving the capacitor open-circuit, and so the DC voltage on the node between the capacitor and the resistor will be 20V. Thus the capacitor is fully charged at the beginning of the transient, and all you are seeing is numerical error in the simulator - you are seeing tiny variations in the voltage and the current oscillation is some kind of trapezoidal integration error at the same magnitude as iabstol (or it might be gmin-related - I didn't check). Probably that would go away if you used method=gear2only on the transient.

    If you want to see the capacitor being charged, you could set ic=0 (initial condition) on the capacitor and then run the transient. That would mean that the voltage between the resistor and capacitor starts the transient at 0V and the capacitor is discharged, so would then charge during the transient.

    Andrew.

  • Leey
    in reply to Andrew Beckett

    Thanks Andrew, it works now.

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