Simulation of CS stage with LTC Spice

Discussion in 'General Electronics Chat' started by Dar89, Jan 9, 2012.

  1. Dar89

    Thread Starter New Member

    Jan 9, 2012
    Hello, I have some difficulties with spice simulation. I want simulate the input-output characteristic of a common source stage, with diode-connected load. My problem arises because the result of simulation is different from the characteristic (found on every book :) ) of a common source stage, with diode-connected load. In particoular, from the simulation, i see that the device NMOS amplifier, conducts even if its Vgs<Vth (the current in the simulation has a very great magnitude, so i don't think it's a current of weak inversion). Is this a problem of model of device?I attach a pdf with some images. The model i've used is the follow:
    .MODEL nfet NMOS(LEVEL=1, KP=50u, VTO=0.7, LAMBDA=0.01,
    + GAMMA=0.5, PHI=0.7, TOX=15E-9,
    + CJ=4E-4, CJSW=1E-10, MJ=0.5, MJSW=0.5, PB=0.9,
    + CGSO=2.5E-10, CGDO=2.5E-10, CGBO=2.5E-10)
    Can you help me? Thanks.

    P.S. Excuse me for my english. :D
  2. gootee

    Senior Member

    Apr 24, 2007
    It looks like you first need to right-click on those NMOS devices and pick a "real" device from the list of available devices.
  3. Ron H

    AAC Fanatic!

    Apr 14, 2005
    You can't pick a "real" part for a 4-pin MOSFET.
    What he does need to do is right-click on them and change the model names from NMOS to nfet, which is his model name.