pfalstad
commented
5 years ago Hi, I got it from Pillage, "Electronic Circuit & System Simulation Methods", which got it from Muller and Kamins, "Device Electronics for Integrated Circuits".
It's described as the "quadratic model" here: https://ecee.colorado.edu/~bart/book/models.htm . That link doesn't mention beta but it seems to be the same model if you set beta = mu Cox (W/L). It also discusses the variable depletion layer model, which has a varying threshold voltage.
Someone has asked for the EKV model (#21) to be provided as an option, since it's much more accurate and can model things like subthreshold conductance.. And it would also fix your issue as well.
ormaaj
What model describes MOSFET behaviour using a "beta" and a fixed threshold? The few CMOS design textbooks' introductory chapters I looked at always model threshold as a function of the channel dimensions and substrate bias (among other things but those seem to be the most significant parameters). I haven't found a model that approximates a realistic variable threshold like this given a beta parameter and base threshold, though it might be possible since beta is determined by channel W / L.
Evidently some microprocessors use a dynamic body bias in places as a power-saving feature because subthreshold current is a function of the threshold voltage, which is a function of body-source voltage for a given Vds, so they can cut down on leakage in unused parts of a circuit.
Not that we really care about subthreshold action... There are probably better examples of where this matters, like maybe some N-ary logic could exploit that.