PSPICE CS Amplifier, please help!

Discussion in 'Homework Help' started by Renton, Apr 30, 2008.

  1. Renton

    Thread Starter Member

    Apr 21, 2008
    I attached to this post my common source amplifier that I built with the directions given in my book. It is supposed to give a voltage gain of 10, but it's more like 2. I haven't changed any internal parameters of the transistor yet except fo the L and W(not sure what M is). What values in the circuit can I change to get a gain closer to 200?

    Thank you for any help!
  2. Audioguru


    Dec 20, 2007
    What is the resistance of R1 and R4?
    I have never heard of 2E6 and 1.3E6.

    Does the Mosfet conduct any current with such a small gate to source voltage?
  3. Renton

    Thread Starter Member

    Apr 21, 2008
    I assmued the 2E6 meant 2000000, but I'm not sure since the book doesn't say, for some reason. The MOSFET conducts very little current, now that you mention it. Is there anything you can suggest I change to get a bigger gain?

  4. Caveman

    Senior Member

    Apr 15, 2008
    2E6 is 2Meg and 1.3E6 is 1.3Meg.
    You likely need to increase the V1 voltage. This will turn it on into the active mode. You are likely in cutoff here. I'm not sure how much since I'm not immediately familiar with the spice MOSFET model terms M, W, and L.
  5. vivekniwane

    New Member

    May 4, 2008
    It' all OK to have resistors in the design.
    But if circuit is to be implemented using only MOS then we have to play with Id, W/L
    and Vgs. It, too difficult for me to have this design.
    Can any one suggest me the right design steps for it?

    Thank You.