Weak Inversion Model of an Inverting CMOS Schmitt Trigger

In this article the subthreshold characteristics of an inverting single input CMOS Schmitt trigger circuit are analyzed. Analytical expressions for the low-to-high and high-to-low hysteresis transition voltages are determined. The analytical model provides physical insight into the circuit behavior. The derived expressions are linearly dependent on the supply voltage and the temperature, and logarithmically dependent on the dimensions of the transistors. Simulation results validated the proposed model, with a maximum error between the analytical and simulated transition points smaller than 14mV. An ASIC in AMS 0.35μm CMOS process has been fabricated to experimentally validate the derived expressions. The maximum error between the analytical and measured transition points is below 36mV.