bjt amplifier in pspice

Discussion in 'General Electronics Chat' started by Hooman95, Mar 4, 2014.

  1. Hooman95

    Thread Starter New Member

    Mar 4, 2014
    3
    0
    Hello. I'm going to design a simple bjt amplifier with a CC stage and a CE stage in Pspice.
    But, How can psice calculate the gain, I mean in a way exept of looking at the out put graph and guess the voltage gain.
    How could I do AC sweep?
    Can anyone give me a spice toturial for amplifiers? because most of pspice toturials I've found, generally discuss about RC circuits, make a new project,..

    thanks
     
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  2. crutschow

    Expert

    Mar 14, 2008
    13,021
    3,235
    You can calculate the gain by dividing the output AC voltage by the input source AC voltage. No guessing involved. (I assume there are cursors available for the plots that give you the exact voltages). If the plots allow waveform arithmetic then you can plot V(out)/ V(in) where out and in are the output and input nodes respectively.

    If you want the gain versus frequency then do an AC analysis over the frequency range of interest.
     
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  3. shteii01

    AAC Fanatic!

    Feb 19, 2010
    3,393
    497
    A more basic ilustration:
    Output=Gain*Input
    You know the Input, because you set it up.
    You know the Output, because you measured it.
    Solve for Gain. What could be simpler?
     
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  4. mvaseem

    Member

    Jan 31, 2014
    48
    8
    If you want to use AC analysis for gain measurement, do following -

    - Replace V3 source in your schematic with AC source (VAC from source.olb)
    - Do AC analysis in the frequency range of interest. Go to following link to see how to do AC analysis (page 322)- http://www.ing.unitn.it/~fontana/spiceman/AC_Analysis.pdf

    - Plot the output node. Since AC input amplitude is 1 by default, the output (at low freq) would give you gain. You can also figure out the bandwidth of amplifier by that method.

    If you want to use transient analysis for gain measurement, do following -

    - Replave V3 by VSIN from source.olb. Provide small signal amplitude (like 1mV), freq of interest, Offset (typically 0).

    - Do transient simulation for time to have couple of cycles. Following link - http://www.csun.edu/~apr69082/PSpice/bjttransient.html
    - Plot output node.
    - Divide output amplitude with input amplitude to get gain.
     
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  5. Hooman95

    Thread Starter New Member

    Mar 4, 2014
    3
    0
    Hi mvaseem. your guides was helpful. the pages you attached seems to be chosen from a good book. woud you send me a link to download the book?
    thanks
     
  6. Hooman95

    Thread Starter New Member

    Mar 4, 2014
    3
    0
    I mean without using corsurs and deviding output amplitude over the input, how pspice itself computes the voltage gain?
     
  7. LvW

    Active Member

    Jun 13, 2013
    674
    100
    PSpice is a circuit simulation program - and as such it calculates voltages and currents.
    However, the display unit (PROBE) is able to show the ratio of two such quantities.
    If you know how the term "gain" is defined, it should be possible to display the wanted ratio.
     
  8. mvaseem

    Member

    Jan 31, 2014
    48
    8
    Hi Hooman,

    I just did the google search for the links. One of them is basically a pspice user guide. If you have pspice installation, it would be located at - <install>/doc/pspug/pspug.pdf.

    For AC analysis, since input AC manitude is 1, pspice would give you gain by directly plotting Vout.
    There are predefined templates also available in pspice. The template - "Bode Plot dB" would give you gain and phase for Vout.

    You can also create measurements and macros where you can save all the calculated (divide traces, multiply etc) expressions and just reload them after simulation.


    -mvaseem
     
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  9. crutschow

    Expert

    Mar 14, 2008
    13,021
    3,235
    As mvaseem noted, if you use a value of 1 for the source in an AC analysis then the output directly equals the gain in dB since the output is plotted with a reference value of 1 for the dB calculation (or dBV).
     
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