Can't figure out PMOS small signal

Discussion in 'Homework Help' started by doze, Feb 28, 2013.

  1. doze

    Thread Starter New Member

    Feb 10, 2013
    9
    0
    I have a hard time analyzing small signal for PMOS. I have seen that you reverse the voltages and saturation equation but that is just with biasing it. I am still confused on how to deal with small signal. I am using the Razavi Fundamentals of Microelectronics and it uses the NMOS small signal for the PMOS small signal. How can this make any sense.

    How do I draw out the small signal for PMOS for pi model and t-model. I am trying to analyze the attached circuit to get the gain. I think using t-model would be easier but I also want to know how to use pi-model.
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,056
    3,245
    Small-signal ignores the DC bias conditions so it makes no difference if it's a PMOS transistor or an NMOS transistor for small signal calculations. Both NMOS and PMOS transistors amplify the same for small AC signals.
     
  3. doze

    Thread Starter New Member

    Feb 10, 2013
    9
    0
    Yes but how do I treat their small signal. I haven't done enough of these to where I can just solve it by inspection so I have to draw out their small signal by hand. I know Vgs become Vsg but in my books, the treat the small signals as if they are the same
     
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