Hand analysis of metal-oxide semiconductor field-effect transistor (MOSFET) circuits usually is based on a rather simplified small-signal circuit. In debugging a design and checking whether errors of analysis have crept in, it is handy to be able to compare the hand analysis with a realistic circuit simulation. For MOSFETs, a realistic model is the Berkeley short-channel insulated-gate field-effect transistor (IGFET) model (BSIM) 2, 3, which has parameters for various technology generations readily available on line from MOSIS 4. Unfortunately, the textbook small-signal circuit, regardless of the choice of parameters, does not fit the BSIM because it is oversimplified 5, Fig. 4.47(c), 6, which raises problems in trying to identify whether an error has occurred, and a crisis of confidence in the validity of the approach. Here we show that a small-signal circuit devised by Liu 1, p. 135 enables both hand analysis and also agreement with the BSIM.
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