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Questions about Modified Nodal Analysis

Discussion in 'CAD' started by Dilips, Nov 23, 2006.

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  1. Dilips

    Dilips Guest

    Hello Everybody,

    Can you please help me out with a few answers about modified nodal
    I have read the book by Kishore Singhal and Vlach.
    1. Does MNA(modified nodal analysis) solve non-linear circuits too?
    inlcuding a transistor?
    2. Where can I get a Code C++ or matlab for the MNA procedure.(where i
    can input a circuit netlist and get the matrix)
    3. will the matrix formed by MNA be in symbolic form or will it be in
    the form of numbers?

    Any help will be greatly appreciated.

  2. The public domain SPICE source code was originally written in Fortran.
    If you look say, in the ASME website you can find the different
    versions. Later code is C generated from passing this code with
    additions through a Fortran to C preprocessor. It is almost entirely
    un-readable IMHO. From this you should be able to answer your various
    questions. IMHO the stuff should be rewritten (that is the core code) in
    a more readable format and then made into an open source project. I
    could suggest using regular expressions to make the parser work a bit
    better. The matrix solver could be reworked for more performance. Doing
    this sort of stuff could benefit the whole SPICE community. As it is all
    modifications seem to be hidden inside commercial software. Improvements
    like better dealing with RF modelling would then trickle down to the
    users of the cheap packages. As it is a good RF package runs a bare
    minimum of $1000US ex. Microwave Office, Eagleware Genesys, Agilent ADS.
    As it is SPICE class modifications which can do 2D EM modelling would be
    really cool to add IMHO. This stuff in Microwave Office for IC design
    runs up to big dollars.

    Good Luck in your Endeavours!
  3. Dilips

    Dilips Guest

    Thanks for the comment Andrew.
    Yes, I am actually trying to write the MNA in C++ myself.
    I am writing it as part of a tool I am creating which can predict about
    Though it is not a great tool, its just part of my research.

    Thank you for your reply,
  4. Joel Kolstad

    Joel Kolstad Guest

    It's part of the solution: Solving an MNA matrix becomes the inner part of a
    loop that attempts to figure out the correct bias point of all your non-linear
    devices. From that bias point, you generate an MNA matrix using the
    linearized equations describing your non-linear device. The "loop" is just
    Newton-Raphson iteration... applied to the MNA matrix (recall that "regular"
    Newton-Raphson is a method for solving an arbitrary equation f(x)=y -- which
    is often non-linear -- using only linear methods).
    Hmm... I'm not sure, although I can tell you that in the class I took on
    circuit simulators, we all wrote our own and it didn't take too long to do so
    (it was something like... week 1... write the parser for the netlist, week 2
    get it to work with DC sources and RLCs, week 3 get it to work with dependent
    sources and AC, week 4 add a diode and a transistor, week 5 add transient
    analysis, etc.). You were allowed to use your programming language of choice,
    and since at the time almost everyone was using C I decided to be different
    and used "legitimate" object-oriented C++ for mine, although I was sorely
    tempted to use Matlab instead (the main reason I didn't is because we used the
    a public-domain sparse matrix package written in C that not only handled all
    the memory management for you but solved Ax=b as well... nice! ...although
    Matlab has sparse matrix support built-in, it still would have been a bit more

    The class was taught by Dr. Karti Mayaram, who definitely knew what he was
    talking about (not to mention being a nice guy). Hmm... looks like he's
    teaching it this quarter as well, here's the web page: . Some of the student
    projects were quite impressive... I just did some lame circuit modelling
    stuff, but others implemented fancy things like harmonic balance simulators.
    Numbers. Conceptually you can use the symbolic form, but even with a powerful
    computer algebra system such as the one in Maple or Mathematica, in most cases
    you won't be able to derive a closed-form solution for anything but trivial

  5. Robert

    Robert Guest

    As I vaguely remember from the class I took, there were other, more recent,
    algorithms for Non-Linear Equations as well as the standard Newton-Raphson.
    But it was hard to beat Newton-Raphson for speed and robustness. Though as I
    understand it has connections to Dynamical Systems and Chaos.

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