Logic Gates

Digital circuit logic gates have a high or low output that is determined by the high or low voltage at the input(s). The NOT gate is the only logic gate with  1 input. All the other logic gates have 2 or more inputs.

NOT Gate:

NOT Logic Gate Schematic Symbol and Truth Table Diagram by Electronzap
NOT Logic Gate Schematic Symbol and Truth Table Diagram by Electronzap

The Output is the opposite state of the input.

  • High input = Low output.
  • Low input = High output.

The Schmitt Trigger version has an extra symbol in the middle of the NOT gate symbol. Some circuits depend on the Schmitt trigger circuitry. to work properly.

AND Gate:

AND Gate Schematic Symbol and Truth Table diagram by Electronzap
AND Gate Schematic Symbol and Truth Table diagram by Electronzap

The AND gate comes with 2 or more inputs. 2 inputs is most common.

If any, or all of those inputs are low, then the output is low.

Every output needs to be high for the output to be high.

NAND Gate:

Basic NAND Logic Gate Schematic Symbol and Truth Table by Electronzap
Basic NAND Logic Gate Schematic Symbol and Truth Table by Electronzap

NAND gates have an output that is only low if all inputs are high. If one or more inputs are low, then the output is high.

The NAND gate is the inverse (opposite) of the AND gate.

The NAND gate is a universal logic gate. You you have enough NAND gates, you can make any other logic gate with them.

OR Gate:

Basic OR Logic Gate Schematic Symbol and Truth Table Diagram by Electronzap
Basic OR Logic Gate Schematic Symbol and Truth Table Diagram by Electronzap

OR gates only have a low output if all inputs are low.

If one or more input is high, then the output is high.

NOR Gate:

Basic NOR Logic Gate Schematic Symbol and Truth Table diagram by Electronzap
Basic NOR Logic Gate Schematic Symbol and Truth Table diagram by Electronzap

The NOR Gate is the inverse (opposite) of the OR Gate.

When the NOR Gate inputs are both low, the output is high. But when one or more inputs are high, then the output is low.

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