MOSFET feedback_bias circuit...stuck

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

  1. csmain

    Thread Starter New Member

    Mar 28, 2009
    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 ?


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


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

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


  2. Ataleph

    Active Member

    Apr 20, 2009
    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
    thanks for the reply..