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Problem with initial conditions for large Capacitor value

palz

Hi,

I am quite new to Cadence spectre. I was trying to simulate a simple RC circuit (with time constant 0.05 s ) with sinusoidal input supply with frequency of 250 Hz.

I have a problem with the initial conditions in the capacitor. The initial condition seems to be ignored when the capacitor value is greater than 1 mF.
What could be the problem?  Kindly help me find a solution to this issue.

Parents
  • Frank Wiedmann

    Your problem is not the large capacitor value but the small resistor value. Quoting from the Spectre User Guide (support.cadence.com/.../cos;src=pubs;releaseName=;DocumentType=manuals;q=/spectreuser/spectreuser15.1/chap17.html#297523):

    The Spectre simulator sets initial conditions on a node by attaching a voltage source through a resistor. The default value of this resistor is 1, but you can control the value through the options parameter rforce. You can lower the value of rforce to bring the voltage values into agreement in one of the following ways:

    • Through the Analog Options window in the Analog Design Environment (Simulation -> Options -> Analog -> Algorithm)
    • Inserting an options statement in the netlist. An example is given below:

    myOptions options rforce=1m

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  • Frank Wiedmann

    Your problem is not the large capacitor value but the small resistor value. Quoting from the Spectre User Guide (support.cadence.com/.../cos;src=pubs;releaseName=;DocumentType=manuals;q=/spectreuser/spectreuser15.1/chap17.html#297523):

    The Spectre simulator sets initial conditions on a node by attaching a voltage source through a resistor. The default value of this resistor is 1, but you can control the value through the options parameter rforce. You can lower the value of rforce to bring the voltage values into agreement in one of the following ways:

    • Through the Analog Options window in the Analog Design Environment (Simulation -> Options -> Analog -> Algorithm)
    • Inserting an options statement in the netlist. An example is given below:

    myOptions options rforce=1m

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