Need Some Pointers Regarding LTspice

Discussion in 'Analog & Mixed-Signal Design' started by elec_eng_55, Sep 7, 2018.

  1. elec_eng_55

    Thread Starter Member

    May 13, 2018
    87
    0
    Hi:

    I would like to know how to add directives for calculating ac gain for
    the attached circuit.

    Also, Is it necessary to constantly open the Simulator Edit mode
    prior to running a sim? I have a feeling that I am missing some
    step.
    upload_2018-9-7_18-44-44.png


    Thanks,

    David
     
  2. crutschow

    Expert

    Mar 14, 2008
    19,519
    5,444
    If you set the AC voltage of Vin to 1V and run the AC analysis, you will get a plot of the output gain versus frequency directly in dB (0dB being a gain of 1). See below:

    upload_2018-9-7_21-41-16.png

    No.
    I run an analysis by right-clicking anywhere in the schematic and selecting "Run".
     
    Last edited: Sep 8, 2018
  3. Jony130

    AAC Fanatic!

    Feb 17, 2009
    4,461
    1,262
    But we can also change the Y-axis and plot Y-axis in "linear mode"( AC voltage set to 1V)

    1.png

    We can do that because AC analysis doesn't take into account the power supply limitations ( AC analysis is using linearized small-signal model for all of the nonlinear devices).
     
  4. elec_eng_55

    Thread Starter Member

    May 13, 2018
    87
    0
    Hi:

    How do you get a nice graph like this?
     
  5. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    What do you mean by "nice graph"? The background color?
     
  6. elec_eng_55

    Thread Starter Member

    May 13, 2018
    87
    0
    I mean what directives do you use to obtain a graph like this?
    The help files for Spice are garbage.

    David
     
  7. Jony130

    AAC Fanatic!

    Feb 17, 2009
    4,461
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    Non

    I simply set the AC analysis

    2.png

    Set the AC source to 1V

    And run the simulation and plot the output voltage.

    Then I clik right muse batton ont the vertical axis and change to use a Linear
    3.png
     
  8. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Let's just say they are 'concise'. Did you read the Waveform Viewer Help?
     
  9. Janis59

    Active Member

    Aug 21, 2017
    561
    84
    RE: ""The help files for Spice are garbage.""
    INTO Spice it is really like just the shortest memo and no more
    For normal lead-in course You ought go to their site and download the handbook. I clearly dont remember from where I got one, but at mine is over 1000 pages of detailed explanations. I may claim it is sure too much detailed :)
     
  10. elec_eng_55

    Thread Starter Member

    May 13, 2018
    87
    0

    Thank you for all your replies!
     
  11. DickCappels

    Moderator

    Aug 21, 2008
    4,863
    1,470
    1,000 pages sounds comprehensive. What is the name of that manual? Was it a book you had to buy?

    Some searches turned up about 150 pages and about 250 pages, but nothing like 1,000 pages.
     
  12. Janis59

    Active Member

    Aug 21, 2017
    561
    84
    Somewhere downloaded in torrents. If memory not fails, it was Wiley or at least Elsevier product.
     
    DickCappels likes this.
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