High frequency MOSFET amplifier , CS with Rs

Discussion in 'Homework Help' started by greenland, May 22, 2018.

  1. greenland

    Thread Starter New Member

    Jan 28, 2018
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    0
    3.png
    a) AM=? (when Cgs and Cgd are 0) --> AM = -gmRL / (1+gmRs)
    b) ωH=? (using OCTC method)
    Rgs =? Rgd=?
    I'm stacked on this point.
    In the case of CS MOSFET without Rs:
    Rgs=Rsig
    Rgd= Rsig(1+gmRL)+RL

    What will change in CS MOSFET with Rs?

    I'd really appreciate any help. Thanks in advance.
     
  2. Jony130

    AAC Fanatic!

    Feb 17, 2009
    4,461
    1,262
    You need to solve this circuit

    12a.png

    If you whant to find Rgs seen by Cgs capacitor.

    Rgs = Vx/Ix

    Also notice that now Vgs = Vx and Is = Id - Ix.

    Can you solve it ?


    As for Rgd resistance seen by Cgd capacitor, you need to solve this circuit:

    12b.png

    And once again

    Rgd = Vx/Ix
     
    Last edited: May 23, 2018
    greenland likes this.
  3. greenland

    Thread Starter New Member

    Jan 28, 2018
    7
    0

    VG = Vgs + gmVgsRs
    VG = IxRsig
    Vgs = IxRsig / (1+gmRs)

    Vx= VG -VD=IxRsig - (-IDRD) = IxRsig + (Ix + gmVgs)RD = Ix(Rsig + RD) + gmVgsRD
    Vx / Ix = Rsig + RD + gmVgsRD / Ix

    => Rgd = Rsig + R
    D + gmRsigRD / (1 + gmRs) = Rsig + RD ( 1 + gmRsig / 1+gmRs )


    Thanks a lot. I find it really helpful.:)
     
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