Q10CMOS Design

Body effect refers to the phenomenon in which a MOSFET's threshold voltage changes (increases in magnitude) when a non-zero, reverse-biasing voltage exists between the source and the body (substrate) terminals, Vsb, rather than the source and body being tied to the same potential as commonly assumed in simplified analysis - this occurs because a reverse-biased source-body junction widens the depletion region beneath the gate, requiring additional gate voltage to support this larger depletion charge before the channel can be inverted, following the relation Vt=Vt0+gamma(sqrt(2phi_f+Vsb)-sqrt(2*phi_f)), where gamma is the body-effect coefficient and phi_f is the Fermi potential - body effect is a particularly important consideration when analyzing series-stacked transistors (such as in a NAND gate's series NMOS pull-down network) or source-follower configurations, where internal transistors do not have their source directly tied to ground/body potential.