MOSFET feedback_bias circuit...stuck

Discussion in 'Homework Help' started by csmain, Apr 22, 2009.

  1. csmain

    Thread Starter New Member

    Mar 28, 2009
    6
    0
    Im stuck on this problem and have been trying to figure it out...could someone show me what to do...any help appreciated

    Fig. 3 shows a feedback‐bias circuit. You are provided a 6‐V power supply and NMOS transistor(VT=1.2 V, K=1.6 mA/V2). Provide a design which will bias the NMOS transistor at ID= 2mA, with VDS large enough to allow saturation operation for a 2‐V negative signal swing at the drain. Use 22 Mohm as the largest resistor in the feedback‐bias network. What are the values for RD, RG1,RG2 ?

    //work

    Vds= 6-Rd(Id+I) Set Rg1 = 22M ohm

    Id=k(Vgs-Vt)^2

    .002 = .0016/2(Vgs-1.2)^2 =>Vgs=2.32V

    Vgs=Vds(22M/(22M + Rg2))

    I=Vds/Rg1+Rg2

    Untitled.jpg
     
  2. Ataleph

    Active Member

    Apr 20, 2009
    31
    0
    According to the figure this equation should be changed to
    Vgs=Vds(Rg2/(22M + Rg2))
    Additionally try to use the "2‐V negative signal swing at the drain".
    I think the drain voltage must be set to a value between the power supply and 2V (3.5V for example). That would give you Vds => you have now 3 equations with 3 variables => can solve.
     
  3. csmain

    Thread Starter New Member

    Mar 28, 2009
    6
    0
    thanks for the reply..
     
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