Sedra Smith, Ch6, ex 6.5

Discussion in 'Homework Help' started by yitch, Sep 25, 2010.

  1. yitch

    Thread Starter New Member

    Jun 27, 2010
    8
    0
    Hi,

    I'm lost as to how to begin, The VGS is not given, how would one be able to solve for the W?

    And I subbed in the value of W1 into the current steering equations, I2 and I3 are a magnitude of .1 from the answer and I5 is totally off the mark.

    I have attached the images, pls help :(

    Thanks!
     
  2. Ghar

    Active Member

    Mar 8, 2010
    655
    72
    You find Vgs from the requirement of swing.

    For saturation, which is the requirement for a MOSFET acting as a current source:
    Vds > Vgs - Vth

    You want drain of Q2 to go within 0.2V of -Vss, meaning you want the transistor to stay in saturation even with a Vds of 0.2V.

    This gives:

    Vgs - Vth < 0.2V
    Vgs < 0.8V

    Plug that into the current equation:

    I_D = \frac{1}{2}k_n'\frac{W}{L}(V_{gs} - V{tn})^2\\<br />
10\mu = \frac{1}{2}200\mu\cdot\frac{W}{1\mu}(0.8 - 0.6)^2\\<br />
0.1 \mu= W 0.04\\<br />
W = 2.5\mu

    Similarly you do that for the PMOS to get W4.
     
  3. yitch

    Thread Starter New Member

    Jun 27, 2010
    8
    0
    Ah... ok


    thanks!
     
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