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Simple spice 3 question

Discussion in 'CAD' started by [email protected], Mar 5, 2006.

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  1. Guest

    Hi, the spice 3 manual
    says this:

    DC/TRAN is the dc and transient analysis value of the source. If the
    source value is zero both for dc and transient analyses, this value may
    be omitted. If the source value is time-invariant (e.g., a power
    supply), then the value may optionally be preceded by the letters DC.
    Any independent source can be assigned a time-dependent value for
    transient analysis. If a source is assigned a time-dependent value, the
    time-zero value is used for dc analysis.

    But then it gives the following examples:
    VIN 13 2 0.001 AC 1 SIN(0 1 1MEG)

    I don't understand why they specify 0.001. The text says the time-zero
    value of the sin() function will be used as the value for dc
    simulation, so I'm wondering if the 0.001 is for something other than
    the dc value. Or is the 0.001 used when *only* a dc bias point is
    requested, but the sin() time-zero value is used for bias point when a
    transient is requested elsewhere in the simulation? Which of these is
    used as bias setup for AC sim?

    Also, from the first paragraph, am I to infer that you may not use 'DC'
    if the source is time-variant? I realize the logic doesn't say this
    explicitly (modus ponens and all that), but I'm wondering anyway.

    Also, can the dc transient definition be swapped in position with the
    ac and distof1 definitions? Their example suggests yes, but it doesn't
    quite conform to the canonical structure as listed in the definition of
    vxxxx and ixxxx.

    Why all this? I'm writing my own spice parser... for fun :)
    BTW, other than the source code and user documentation, is there a
    place where the spice syntax is defined more formally, such as
    backus-naur form? That might answer some questions.

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