NAND gate

Shihab Uddin Ahmed | February 6, 2017

AND, OR and NOT are three basic operations in Boolean algebra; and AND, OR and NOT gates are three basic gates in digital electronics. Actually all logic gates are made of these three gates.

Definition of NAND operation

NAND operation is a Boolean operation where output is false only if all operands are true.

In terms of NAND gate

NAND gate circuit is a logic circuit where output is always one except when all inputs are one.

Two input NAND gate symbol photo

Two input NAND gate symbol

Two input NAND gate truth table photo

Two input NAND gate truth table

There is an important point to note in the truth table above. At first we may consider AND operation on two operands (inputs) A and B, after that we are inverting the result with NOT operation. This is how NAND gate works.

NAND gate in simple words

NAND gate is like connecting an AND gate output to a NOT gate input like the figure below:

AND-and-NOT-gate-make-NAND-gate photo

NAND gate may have three or more inputs

Three input NAND gate symbol photo

Three input NAND gate symbol

Boolean expression for NAND gate operation which is read as x = not A.B,

Boolean expression for NAND gate operation photo

NAND and NOR gates are called universal gate because you can construct any gate using NAND gate or NOR gate.

Circuit diagram of a NAND gate using transistors and resistors photo

Circuit diagram of a NAND gate using transistors and resistors

In the circuit diagram above you will notice that output is always high except when both transistors are biased. It’s possible only when both inputs are high.

NAND gate IC

Various NAND gate ICs are available in market, 7400 is one of them. It’s a 14 pin two input NAND gate IC where four NAND gates are packed. It works on 5 volt power supply.

7400 IC

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