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Homework Help: Semiconductor Voltage Output

  1. Nov 14, 2011 #1
    Hi all, this is my first post here. I'm hoping some input will help me verify what I am missing.

    This is a question from an exam paper I'm doing for a module on introduction to semiconductor technology

    Calculate the CMOS inverter output voltage Vout, and the corresponding inverter current,
    for each of the following inverter input voltages:
    Vin = 1V
    Vin = 4V
    Vin = Vout = Vinv (inverter switching voltage)
    where the CMOS transistor parameters are as follows:
    Vthpd= -Vthpu=0.7V, Wpd/Lpd=2, Wpu/Lpu=4, μn=2μp, Vdd=3.5V
    Clearly state (and verify) all assumptions.

    The issue is less with the question, more with the sample solution that the lecturer has given, where he provides some assumptions, which has confused my previous understanding:

    Assume Vdspd ~ .3V, Vdspu = .3-3.5 = -3.2V
    Vdsatpd = Vgspd-Vthpd = 2.1 - .7 = 1.4 => in linear operation (to be verified after calculation)
    Vdsatpu = Vgspu-Vthpu = 2.1-3.5+.7 = -.7 => in satn operation (to be verified after calculation)

    I'm confused as to where he obtained the value '2.1'. I understand everything else with regards to equating the linear or saturated I-V MOSFET equations and proceeding from there, but I think I'm missing something rather basic here... go easy lol....
  2. jcsd
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