CMOS Inverter Electronics Question

Discussion in 'Homework Help' started by jegues, Nov 29, 2011.

  1. jegues

    Thread Starter Well-Known Member

    Sep 13, 2010
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    I'm having trouble with this question. (See figure attached)

    How do I go about showing that the expression provided is indeed the maximum current that the inverter can sink under the mentioned constraints?

    After I figure that part out I will make an attempt at the second portion of the question.

    Thanks again!
     
  2. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    I don't see any work from you, only scans from a bookk?

    Show your attempt at it, please.
     
  3. jegues

    Thread Starter Well-Known Member

    Sep 13, 2010
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    i_{dmax} = 0.075kn'(\frac{W}{L})_{n}V_{DD}^{2}

    V_{OL} = 0.1V_{DD}

    To be honest with you, I don't have a good enough feel of where to start to give any reasonable attempt.

    Can you give me a shove in the right direction?

    I have no problems with making attempts at the solution as long as I have something to work from.
     
  4. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    I believe you are to work the given answer backwards from the end where it is stated that k^'_n=\frac{115\mu A}{V^2} @V_{DD}=2.5V

    Make a simultaneous equation to find (\frac{W}{L})_n while current is 7.5mA

    Since, as I read it, the technology at 0.2V_{DD} allows 7.5mA with that same k'_n

    That's my shot in the dark, it's been a while since college, and there are several statements intermixed with questions in that little paragraph they show.

    Are the terms or methods of deriving K'_n and  \frac{W}{L} defined somewhere on that same page outside of this question?
     
  5. jegues

    Thread Starter Well-Known Member

    Sep 13, 2010
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    Before making equations for W/L I need to show how the equation they've given me comes to be.

    That's what I'm trying to figure out before I crunch out W/L.
     
  6. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    I thought (hoped?) that would have been covered in the book or in class.

    I guess we need to wait for t_n_k to arrive. :D
     
  7. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    Use the general relationship

    I_D=\frac{K'W}{L}\[(V_{GS}-V_T)V_{DS}  -\frac{V_{DS}^2}{2}\]

    For the NMOS on state ...

    Substitute

    V_{GS}=V_{DD}, \ V_T=0.2V_{DD}\ & \ V_{DS} =0.1V_{DD}

    and you should obtain the required relationship.
     
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