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PSpice Convergence Problem

Discussion in 'CAD' started by Bob Penoyer, Sep 15, 2005.

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  1. Bob Penoyer

    Bob Penoyer Guest

    I have a circuit comprising one OP-77/AD op-amp that is basically a
    Sallen-Key filter with some other resistors and capacitors around it.
    All capacitors use a tolerance (10%) and all resistors use both a
    tolerance (1%) and a tempco (100 ppm/C).

    I've had convergence problems during worst-case simulations at some
    temperatures. The OP-77/AD seems to be at the heart of the problem but
    I'm stuck with it because I'm analyzing an existing circuit.

    All of the power supplies (+/-15V for the op-amp, and +5 for another
    item) have both 5% voltage tolerances and 200 mVpp noise at 20 kHz
    bandwidth.

    I've made these modifications to the default simulation settings:
    VNTOL = 1E-4
    ABSTOL = 1E-10
    GMIN = 1E-9
    ITL1 = 5000
    ITL2 = 2000
    ITL4 = 2000

    Is there something else I should do to enhance convergence?

    What about the solver? Is the default best? What are solver 0 and
    solver 1?

    Is selecting GMIN stepping helpful?

    Thanks,

    Bob Penoyer
     
  2. Jim Thompson

    Jim Thompson Guest

    SOLVER=0 is the old original solver before it was "new and improved".
    I have found the setting SOLVER=0 will often work on difficult
    circuits.
    Sometimes ;-)

    ...Jim Thompson
     
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