Propagation of digital signals under the influence of noise, the Noise Margin High is V(OH) V(IL) V(OL) V(IH)( V(OH), V(IL), V(OL), V(IH) ) minus V(IH) V(OH) V(IL) V(OL)( V(IH), V(OH), V(IL), V(OL) ) and, the Noise Margin Low is V(IL) V(IH) V(OL) V(OH)( V(IL), V(IH), V(OL), V(OH) ) minus V(OL) V(OH) V(IH) V(IL)( V(OL), V(OH), V(IH), V(IL) ).

For CMOS Inverter Circuit, when Input is 1, the Output is 0 and the PUN PDN( PUN, PDN ) is off; when Input is 0, the Output is 1 and the PDN PUN( PDN, PUN ) is off.