+ Post New Thread
Results 1 to 6 of 6
  1. #1
    Member level 4
    Points: 2,589, Level: 11

    Join Date
    Jun 2005
    Posts
    76
    Helped
    3 / 3
    Points
    2,589
    Level
    11

    transit frequency

    Hi,
    In Razavi, Problem 2.13 (page 40):
    " The transit frequency of a MOSFET is defined as the frequency at which the small-signal current gain of the device drops to unity while the source and drain terminals are held at ground".
    How can there be current in the transistor when Vsource=Vdrain=0V?
    As far as I know, this is defined as triode region with 0 current. How can there be current gain?

    Thanks in advance for your help.

    •   AltAdvertisement

        
       

  2. #2
    Member level 4
    Points: 2,589, Level: 11

    Join Date
    Jun 2005
    Posts
    76
    Helped
    3 / 3
    Points
    2,589
    Level
    11

    transit frequency mosfet

    And another question: What's the importance of this frequency? How should it be taken into account when designing a circuit?



    •   AltAdvertisement

        
       

  3. #3
    Junior Member level 3
    Points: 1,521, Level: 8
    timer's Avatar
    Join Date
    Aug 2005
    Posts
    30
    Helped
    8 / 8
    Points
    1,521
    Level
    8

    transit frequency

    razavi meant that the drain and source are at signal ground. (something like connecting huge caps from drain to ground). It is assumed that the transistor has been DC biased.

    thats why he says "small-signal current gain".


    2 members found this post helpful.

    •   AltAdvertisement

        
       

  4. #4
    Advanced Member level 1
    Points: 3,359, Level: 13

    Join Date
    May 2004
    Location
    China
    Posts
    422
    Helped
    24 / 24
    Points
    3,359
    Level
    13

    transition frequency mosfet

    THis is the frequency where the transistor can provide current gain. And it's also related to how fast the transistor can be operated.


    3 members found this post helpful.

  5. #5
    Member level 4
    Points: 2,589, Level: 11

    Join Date
    Jun 2005
    Posts
    76
    Helped
    3 / 3
    Points
    2,589
    Level
    11

    transition frequency of mosfet

    Thanks for the answers!



    •   AltAdvertisement

        
       

  6. #6
    Newbie level 6
    Points: 889, Level: 6

    Join Date
    Nov 2010
    Posts
    12
    Helped
    4 / 4
    Points
    889
    Level
    6

    Re: Transit frequency of a MOSFET

    the transit frequency gives the intrinsic (maximum) speed of the mosfet;
    it also means that beyond that frequency the device cant be used as a voltage amplifier;;


    4 members found this post helpful.

--[[ ]]--