MOSFET saturation current

Discussion in 'Homework Help' started by smrams28, Mar 29, 2013.

  1. smrams28

    Thread Starter New Member

    Mar 29, 2013
    13
    0
    Hi. Im a first year engineering student and was having trouble on a problem. I am probably overthinking it.


    Q)The n-channel MOSFET threshold voltage is +2 V. The gate voltage is +4V. The drain voltage is +5V. Is the MOSFET in the current saturation mode?




    I think VGS-VT = VDS for it to be in saturation but this one is not. So is it not in saturation?
     
  2. tshuck

    Well-Known Member

    Oct 18, 2012
    3,531
    675
    Nope. Saturation is:
    provided\ that\ \  V_{GS} \ > \ V_{TH},\ \  then\  V_{DS}\ >\  V_{GS} - V_{TH}

    See here.
     
    smrams28 and screen1988 like this.
  3. smrams28

    Thread Starter New Member

    Mar 29, 2013
    13
    0
    thank you for the link. Very helpful
     
  4. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    What?
    4V>2V
    5V>(4V-2V)

    That looks like saturation to me.
    [​IMG]
     
    screen1988 likes this.
  5. tshuck

    Well-Known Member

    Oct 18, 2012
    3,531
    675
    Wasn't saying that it wasn't in saturation, but that the equation for whether or not it is is wrong. Your red line is the equation in the OP.
     
    screen1988 likes this.
  6. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    OK, I see. The OP thought the expression was an equation, rather than an inequality.
    I saw that, but thought it was just sloppy writing by the OP.:(
     
    screen1988 likes this.
  7. WBahn

    Moderator

    Mar 31, 2012
    17,777
    4,804
    Notice that the OP gave the threshold voltage, the gate voltage, and the drain voltage. They didn't give any indication of the source voltage. Perhaps they mean the other voltages as voltages relative to the source. Perhaps the source is tied to ground. But perhaps niether of these is the case.
     
    screen1988 likes this.
Loading...