Actual gain Vs. Bode plot gain?

Discussion in 'General Electronics Chat' started by Alshatri, Nov 9, 2013.

  1. Alshatri

    Thread Starter New Member

    May 14, 2013
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    0
    Dear all,

    I have the gain @100Khz in bode plot almost=1dB, while the actual gain= 20 log(Vout/Vin)=20 log(3/0.005)= 55.56dB (from the transient values)

    Could someone please explain why I have this weird bode plot gain reading?

    Regards
     
  2. ronv

    AAC Fanatic!

    Nov 12, 2008
    3,281
    1,232
    I think it is because the bode plot is expecting an input of 1 volt so the scale is wrong. I didn't draw it up and try it but I think that's it.
     
  3. Alshatri

    Thread Starter New Member

    May 14, 2013
    4
    0
    Could you tell me please what is the 1V that are you talking about?
     
  4. WBahn

    Moderator

    Mar 31, 2012
    17,715
    4,788
    I think the problem might be related to having a resistor whose value is dependent on the signal. I think the AC analysis linearizes things and so I don't know how it would deal with a voltage-dependent resistance.
     
  5. LvW

    Active Member

    Jun 13, 2013
    674
    100
    Alshatri, when you like to see the gain (Vout/Vin) you must display the ratio Vout/Vin.
    However, your Bode plot shows only Vout.
    Only in case your AC input is 1Volt it is sufficient to display Vout (because it is identical to the gain).
    Remark: I cannot see which resistor value is "dependent on the signal".

    EDIT: Sorry, a sharper look on the drawing has revealed that R3 depends on the input.
     
    Last edited: Nov 10, 2013
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