Length and Width of Transistor(NMOS)

Discussion in 'General Electronics Chat' started by sivaraj, Oct 13, 2007.

  1. sivaraj

    Thread Starter New Member

    Oct 8, 2007
    Hai I am new to design. While I am design a small circuit I got stuck. So pls clarify my droughts.

    I have taken a small ckt. From Microelectronic Circuit by Sedra and Smith. In that I have to find the Width and Length (W/L). I have found the W/L its 10.

    Answer is right in book W/L=10 (W=8um/L=0.8um). But I don’t know how to fix the value for W/L. I mean how much I have to fix for W and for L?

    I know that W=2L, They have given in the that W=8um/L=0.8um.
    Why these much variations. Why we should not take 90um/9um or
    20um/2um ?

    How to fix the value?
  2. Dave

    Retired Moderator

    Nov 17, 2003
    I'm confused by the terminology of "fix the value"; are you looking at fixing the ratio or the physical dimensions? Can I ask which part of Sedra and Smith is the question in so I can have a look and give you further feedback?

  3. sivaraj

    Thread Starter New Member

    Oct 8, 2007
    ya its in the page 265 Sedra&smith question no. D4.11.

    more over, for this question and previous question (Ex 4.3) i have worked. i have designed with W/L 40u/1.2u the output voltage is Vd=0.75, but while i am designing in cadence i am getting 0.2 extra. i dont know why?

    I am designing an CMOS opamp? (current mirror, Diff amp, Active load) i dont know how to design der length and width. can u give mi some idea.