A common drawback of Schmitt triggers is the hysteresis determined by the device dimensions, process parameters and supply voltages(Kuang, and Chuang, 2001).
Current Regenerative Schmitt Triggers With Tunable Hysteresis.
Part 2 of the proposed schmitt trigger consists of a PMOS, (P3) and a NMOS, (N3) where both the MOSFET is directly connected through the gate terminal of each.
By increasing the width of PMOS, it moves the switching threshold voltage towards VDD, which makes the hysteresis width more rectangles as desired by a Schmitt trigger design.
Mentor Graphic has been used to for designing the proposed Schmitt Trigger.