Feedback homework

Discussion in 'Homework Help' started by Rio, Dec 27, 2010.

  1. Rio

    Thread Starter New Member

    Dec 23, 2010
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    0
    hello guys
    i just wanted to show u this circuit that i found in adel sedra's book and i want to know the know how he got the final values and how he got Ic3 ,, any help please cuz we got it as a homework and i don't know how to solve it
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    Last edited: Dec 27, 2010
  2. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    1,097
    Simply post the diagram
     
  3. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    I redrawn the circuit for you.
    Now if you look at circuit B, do you know how to solve it ?
     
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  4. Rio

    Thread Starter New Member

    Dec 23, 2010
    22
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    thanks man thats the circuit with the loading effect
    but the on calculating output DC voltage on 2K
    is it this way : we take 10k parallel with 2k and then the current that flows into the 1.6K is 5mA ?
    and how we calculate the B in this circuit ?
     
  5. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    To simplify the calculation simply assume Vout=0V
    And Ic3=Ie3 = 5mA
    And if we do this, we can simply determine the gain (open loop gain)

    Ao = K1 * K2

    K1 = Rc/2re = ( Rc||( (β+1) * (R1+R2)||RL ) / 2*re2 = 17.876KΩ / 104Ω = 171.885 V/V

    K2 = (R1+R2)||RL / ( re3 +
    (R1+R2)||RL ) = 1.66KΩ / (1.66K +5.2Ω) =0.9968 V/V

    Ao ≈ 171 V/V

    And open loop Rin is equal

    Rin_0 = [ (β+1)*2re] + (R1||R2)/(β+1) = 10.504KΩ + 8.91Ω = 10.51KΩ

    open loop Rout is equal

    Rout_0 = ( Rc /(β+1) + re3 )||(R1+R2) = 199.172Ω
     
  6. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    AS for DC bias point you have to assume β = ∞
    So Ic=Ie
    And then Vout = Vcc - Ic2*Rc - Vbe3
    And that all you have to do
     
  7. Rio

    Thread Starter New Member

    Dec 23, 2010
    22
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    U R a genius MAAN
    thank u very very much and happy new year
     
  8. Jony130

    AAC Fanatic!

    Feb 17, 2009
    3,957
    1,097
    Thx, but you better check my equations, because I wrote them by inspection.

    re = 1/gm = 26mV/Ic

    And voltage gain of a emitter follower is equal

    Au = Re/ (re+ Re)

    And and happy new year for you to.
     
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