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Suppose there is a logic gate and it has two inputs.I want both the inputs to be "high" i.e logic 1, can i have two different voltage values at these two inputs? e.g 3v on one and 4v on another?

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    \$\begingroup\$ This should be directly and clearly answered in the datasheet right where you expect to find it. Look up the input threshold levels. \$\endgroup\$ Mar 18, 2016 at 11:28
  • \$\begingroup\$ what if the two different voltages lie beyond the threshold voltage? \$\endgroup\$ Mar 18, 2016 at 11:47
  • \$\begingroup\$ There is no problem in having different voltage levels on the inputs of a single gate. For each input to be seen as a '1' each voltage must be greater than Vih (max). You did not say what IC this is so I cannot confirm that 3V is adequate to be seen as a '1'. \$\endgroup\$
    – Steve G
    Mar 18, 2016 at 11:51
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    \$\begingroup\$ If the datasheet says that anything over 2.4V is '1' then both inputs are '1'. But if the supply rail is 3V or 3.3V, and the second input isn't "5V tolerant" then 4V will probably destroy the chip. \$\endgroup\$
    – user16324
    Mar 18, 2016 at 12:06

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Read the datasheet.

There will be a spec for the minimum input voltage so that the signal is guaranteed to be interpreted as a logic high. As long as the two inputs meet this criterion, and don't violate any other spec, the logic gate will see both its inputs as high. There is generally no requirement that the two signals be within some voltage of each other, only that each be a valid logic high voltage.

Yes, this really is as simple as it sounds.

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