the cd4093 is a quad two-input nand gate. each input has a schmitt trigger circuit.
the gate switches at different points for positive-going and negative-going signals. the difference between the positive voltage (vt ) and the negative voltage (vt-) is defined as hysteresis voltage (vh).
it operates over a recommended vdd power supply range of 3v to 15v referenced to vss(usually ground). unused inputs must be connected to vdd, vss, or another input.