1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Differential Amplifier with negative feedback

  1. Nov 6, 2017 #1
    1. The problem statement, all variables and given/known data


    2. Relevant equations
    • Adiff(single-ended)= 1/2gm*ro||Rd
    • β=R2/(R1+R2)

    3. The attempt at a solution
    I am really confused as to how to find A. I know the feedback of the circuits around the R2 and R1, but I dont understand how the open loop gain can be found. Can someone assist me in deriving it? First question is what gain are they asking for: common mode or differential? I assume differential, but I am honestly lost.
  2. jcsd
  3. Nov 7, 2017 #2


    User Avatar

    Do you know the meaning of the various given quantities like Vov, VA, ro, RD ?
    Note that the gain is Adiff=0.5*gm*ro||RD.
    Last edited: Nov 7, 2017
  4. Nov 7, 2017 #3
    Yes; my concern is whether the open loop gain(A) is just this equation.

    Also, thanks for the reply!
  5. Nov 7, 2017 #4


    User Avatar

    I have a question to you:
    The first of the "relevant" equations (gain) - did YOU write down the formula or were it given as part of the original text?
    My question is because I do not think that we need this equation.
    So I don`t think we need ro. By the way - what is RD?

    In any case: We need the transconductance gm. From where do we get this value?
    Last edited: Nov 7, 2017
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted