I'm using a logic buffer SN74LVC2G125 (SN74LVC2G125 datasheet) which is powered by 1.8V and has VIH and VIL of 1.17V and 0.63V, respectively.

If I have an input signal like below, could the buffer's output potentially toggle during time intervals B-C and E-F? If not, what are potential negatives that can result from non-monotonic signals crossing VIH and VIL?

enter image description here

  • \$\begingroup\$ Am I reading this right that the input voltage is negative? You'll fry the chip; its absolute maximum limit on any input is no less than -0.5 volts. \$\endgroup\$
    – Hearth
    Jul 9, 2021 at 15:13
  • \$\begingroup\$ @Hearth No, it's just a part of dashed line \$\endgroup\$
    – sp2821
    Jul 9, 2021 at 15:23

1 Answer 1


All that is guaranteed is that any voltage higher than \$V_{IH}\$ is interpreted as a high input, and any voltage lower than \$V_{IL}\$ is interpreted as a low input. All bets are off if \$V_{IL}<V_{in}<V_{IH}\$.

In all likelihood, there will be some voltage somewhere between \$V_{IL}\$ and \$V_{IH}\$ where the input toggles, but what that voltage is--or even whether that voltage is well defined--is not specified.

If you need the output to be in a well-defined state in this condition, you should use a Schmitt trigger. Lots of logic ICs are available with Schmitt trigger inputs, though I don't know if there's an equivalent to the 74xx125 with them. You could always use Schmitt inverters before your '125.


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