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cmos question

Discussion in 'Electronic Design' started by [email protected], Jul 5, 2005.

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  1. Guest

    How do I calculate the drain length Ld of a nmos/pmos? In BSIM3V3,
    there is no parameter Ld.. Can anyone suggest what I can do?

    Thanks,
    Megs.
     
  2. Width and length are user specified values. They are specified on the
    net list line, e.g.

    m1 1 2 3 nmos L=1.2u W=15u

    Some spices (e.g SuperSpice) allow these parameters to be set on the
    schematic via the GUI.

    Ball park values for L and w are often designed from:

    I=K.W/L(Vg-Vt)^2

    More often, one just runs the sim a few times till the numbers are what
    you want:)

    Kevin Aylward

    http://www.anasoft.co.uk
    SuperSpice, a very affordable Mixed-Mode
    Windows Simulator with Schematic Capture,
    Waveform Display, FFT's and Filter Design.
     
  3. Guest

    Thanks for your reply, Kevin.

    Here, in the formula given above, L stands for length of the channel..
    What I am trying to find out is the length of the drain (or source) so
    that I can find the area and perimeter of the drain (and source) .....
    In the tool LTSpice, I have to enter the area and perimeter of the
    drain so that the tool can calculate the capacitances.



    Meghana.
     
  4. Jim Thompson

    Jim Thompson Guest

    Look up HDIF. Generally AD, AS, PD, PS, NRD, & NRS are all calculated
    from L, W & HDIF.

    ...Jim Thompson
     
  5. Guest

    Thanks for replying, James. But here is no HDIF in LTspice (Swcad
    III)...

    Meghana.
     
  6. Jim Thompson

    Jim Thompson Guest

    It's in the device model.

    ...Jim Thompson
     
  7. Yes I missed that point of the post. I have the formulas for the above
    in my SS help file. Of course, in SS you don't need to, its all
    automatic!

    Kevin Aylward

    http://www.anasoft.co.uk
    SuperSpice, a very affordable Mixed-Mode
    Windows Simulator with Schematic Capture,
    Waveform Display, FFT's and Filter Design.
     
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