Input Common-Mode Resistance MOS Diff. Pair

Discussion in 'Homework Help' started by jegues, Oct 14, 2011.

  1. jegues

    Thread Starter Well-Known Member

    Sep 13, 2010
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    How did they come up with that expression for R_{icm}?

    Here's what I came up with,

    R_{icm} = \frac{v_{id}}{i_{b}}

    i_{e} = \frac{v_{id}}{\frac{R_{E} + r_{e}}{2} + R_{EE}}

    i_{e} = (\beta + 1)i_{b}

    \Rightarrow R_{icm} = (\beta + 1)( \frac{R_{E} + r_{e}}{2} + R_{EE})

    Am I doing this incorrectly?
     
  2. jegues

    Thread Starter Well-Known Member

    Sep 13, 2010
    735
    43
    Still looking for clarification on this one.
     
  3. The Electrician

    AAC Fanatic!

    Oct 9, 2007
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    The expression from the book has Rc and ro involved, and you don't.

    Your work involves re, which the book doesn't.
     
  4. jegues

    Thread Starter Well-Known Member

    Sep 13, 2010
    735
    43
    Is mine correct if we were to neglect ro?

    Also where does ro sit? Across Rc or across the collector to emitter?
     
  5. The Electrician

    AAC Fanatic!

    Oct 9, 2007
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    ro is across the collector-emitter.

    The expression in the book appears to be correct with one exception; where they have β they should have β+1. That being the case, I don't think your expression is correct.

    You also have RE and REE; what is RE?
     
    Last edited: Oct 18, 2011
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