A CMOS Schmitt trigger circuit is a really useful block in many ways and has many applications in mixed signal design including oscillators, ( connect a resistor from input to output and a capacitor from the input to ground and oscillations begin easily) signal delay circuits, comparators, logic edge speed up circuits and so on. In a random search for design equations a useful paper turned up written by I.M Filanovsky and H. Bates that provides a set of design equations for Schmitt trigger design. Interestingly this treatment goes beyond the ordinary textbook analysis and provides a more detailed ( in our opinion ) analysis. The design equations were tested using PSPICE simulations and turned out to be quite accurate, The title of the paper is Schmitt Trigger Design, published by the IEEE.. ( IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS-1:FUNDAMENTAL THEORY AND APPLICATIONS, VOL. 41. NO. 1, JANUARY 1994)