CMOS schmitt triggers

Two variants of CMOS Schmitt triggers, consisting of only four enhancement-type MOS transistors, are proposed in the paper. One consists of three NMOS transistors and one PMOS transistor, while the other consists of one NMOS and three PMOS transistors. A Schmitt trigger with three pairs of CMOS transistors is also described. The hysteresis voltage depends on supply voltage and transistor geometry.