Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

PMOS diff amp - common mode input range

  1. Mar 19, 2009 #1

    Can someone help me on how i can calculate the input common mode range for this pmos diff pair. I'd have an idea if it was an NMOS diff pair but am kinda uncertain of this.
    I'm looking for equations for the input signal ranges of Vmax and Vmin


    Attached Files:

  2. jcsd
  3. Mar 20, 2009 #2
    anyone any help on this?

  4. Mar 20, 2009 #3


    User Avatar

    Staff: Mentor

    What are your rail voltages? All that you show so far is the 50uA mirror bias...

    Also, is this coursework? I should move it to the Homework Help forum if it is, and you need to show your own work in order for us to help you.
  5. Mar 20, 2009 #4
    No its not a homework question. just for general use.
    it doesn't mater what the rail voltages are i just want a general equation for the common mode input range for a pmos diff pair

    if it were a nmos diff pair then the eq's would be
    Vin_min = Vds(n6) + Vgs(n1)
    Vin_max = Vaa + Vgs(p3) - Vds(n1) +Vgs(n1)

    where n6 would be the nmos current mirror transistor, N1 - from the diff pair
    p3 - pmos transistor above N1 of diff pair

    so basically i'm just unsure on where the voltage drops are across for when i am using a pmos diff pair.
    I would like help with these equations for the image attached in the first post.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook