Common-Emitter Amplifier With Unstable AC Gain

Discussion in 'Analog & Mixed-Signal Design' started by elec_eng_55, May 13, 2018.

  1. elec_eng_55

    Thread Starter New Member

    May 13, 2018
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    I ran an LTSpice simulation on the attached common-emitter amplifier. The ac voltage gain
    is 10 with input signals between 28mV peak and 148 mV peak.

    When I bread boarded the circuit, the ac voltage gain varied depending on the input
    signal which ranged between 28mV peak and 148 mV peak. Why would the gain
    vary?

    Thanks,

    David
     
  2. crutschow

    Expert

    Mar 14, 2008
    18,620
    5,194
    You are compressing the signal peaks at higher signal levels which makes the gain appear lower.
    Check the bias voltages.
    You need to bias the circuit at a lower emitter and collector voltage (lower values for R5 and R2) to allow more signal output amplitude (dynamic range).
    Ideally you want to bias the collector voltage about midway between the supply voltage and the emitter voltage with an emitter voltage of 2-4V or so.
     
    Last edited: May 13, 2018
    elec_eng_55 likes this.
  3. danadak

    Active Member

    Mar 10, 2018
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  4. Bordodynov

    Well-Known Member

    May 20, 2015
    1,483
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    See
    2018-05-14_16-01-26.png
     
    elec_eng_55 likes this.
  5. elec_eng_55

    Thread Starter New Member

    May 13, 2018
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    Thank You
     
  6. elec_eng_55

    Thread Starter New Member

    May 13, 2018
    4
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  7. elec_eng_55

    Thread Starter New Member

    May 13, 2018
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