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Any frequency sweep feature in LTSpice?

  1. May 20, 2012 #1
    Hi
    I want to find out is there any way to set up frequency sweep in LTSpice and plot the frequency response on a graph? I have look and I cannot find it.

    Thanks

    Alan
     
  2. jcsd
  3. May 20, 2012 #2
    yungman,
    I use LTSpice from time to time, it has all of the usual spice capabilities including AC analysis.

    Click Simulate/Run/AC analysis.

    I have attached a screenshot of what mine looks like.
     

    Attached Files:

  4. May 21, 2012 #3

    vk6kro

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    Science Advisor

    Your signal generator properties must have a voltage entered for small signal analysis.
    Right click on it and look for "AC amplitude" on the right.
    It has to be a sinewave, too.

    You get to AC analysis (on my copy anyway) by using the "simulate" pulldown then "edit simulation cmd" then "AC analysis".

    Click the right scale to turn off phase plotting if it is confusing.
     
  5. May 21, 2012 #4
    Thanks both of you.

    So bottom line is I need to get to "Edit simulation Cmd" and switch to AC analysis instead of Transient analysis.

    Also go to the voltage source and set the amplitude on the AC analysis.

    Thanks

    Alan
     
  6. May 21, 2012 #5
    Most common practice is to set AC amplitude to 1, this way the response you get at any probed point in the circuit will be your transfer function.
     
  7. May 21, 2012 #6

    vk6kro

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    Science Advisor

    When you set the frequency sweep range, LTSpice does not accept MHz as a unit. (Well it does, but it regards it as milli-hertz.)

    So, you need to use E6, (as in 5.5E6 (no space) for 5.5 MHz).
     
  8. May 21, 2012 #7
    Thanks.
     
  9. May 21, 2012 #8
    This is not LTSpice specific.
    Spice uses "meg" as suffix for 10^6, dating back to when Spice was a batch mode fortran program in the 70s.
    Spice is case insensitive so the "m" suffix and the "M" suffix are treated the same (and the Hz is ignored, Spice does not expect units), and both are interpreted as 10^-3 (milli).

    So if you want 10MHz enter 10meg
    if you want 10M ohms enter 10meg
    etc.
     
  10. May 22, 2012 #9

    vk6kro

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    Science Advisor

    Thanks. I'll try that.

    How do you find LTSpice compares with other Spice versions?
     
  11. May 22, 2012 #10
    It is a very decent spice implementation, and pretty easy to learn if you are familiar with traditional spice. Its main appeal is its capability of simulating LT switching regulators.
     
  12. May 23, 2012 #11
    My biggest complain is the pan and zoom. It is hard to control the pan and zoom to get to the right place. I get to spoiled by OrCad schematic and layout that you hit "I" for zoom in and "O" for zoom out. You want to zoom in at one spot, just put the cursor on the spot and hit "I".

    Also the models lack to common op-amp like TLO61, OP07, TLO81, LM324 etc.

    But it gets the job done. This is the only PSpice I ever learn, so I can't compare with the others.
     
  13. May 23, 2012 #12
    Here you can find all the additional models
    http://tech.groups.yahoo.com/group/LTspice/

    http://valvolodin.narod.ru/soft/extra.rar
    http://forest22.homeip.net/Electronics/index.html [Broken]

    Unpack the archive "extra.rar", using the archive RAR
    Copy "extra1.rar" which is installed in the directories are LTspiceIV. Typically, this directory is "C: \ Program Files \ LTC"
    Unzip "extra1.rar" which is installed in the directories are LTspiceIV
    Finish
     
    Last edited by a moderator: May 6, 2017
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