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Noise Margin

  The noise margin is a measure of the extent to which a logic circuit can tolerate noise or unwanted spurious signals. The high state noise margin is defined as

VNH = VOH(min) - VIH(min)

and the low state noise margin is

VNL = VIL(max)- VOL(max)

Thus VNH and VNL give the maximum noise voltage that will not cause incorrect or ambiguous communication of logic level in the H and L states, respectively.


  
Figure 139: Digital voltage levels showing noise margin and error caused by spurious excursion.
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