Nanoscale MOSFET Modeling: Part 2: Using the Inversion Coefficient as the Primary Design Parameter

This article illustrates the use of the inversion coefficient (IC) as the main design parameter to explore the various tradeoffs faced in the design of analog circuits. We start with showing that the same transconductance, gain-bandwidth (GBW) product, or input-referred thermal noise resistance of a common-source (CS) amplifier can be achieved with lower current by shifting the IC toward moderate inversion (MI) at the cost of a slight increase of the transistor aspect ratio and area. In such case the self-loading gate capacitance cannot be ignored, and accounting for it introduces a minimum bias current at an IC that lies in the middle of the MI to achieve a given GBW.