Logic Gates

• The logic gates are the main structural part of a digital system.
• Logic Gates are a block of hardware that produces signals of binary 1 or 0 when input logic requirements are satisfied.
• Each gate has a distinct graphic symbol, and its operation can be described by means of algebraic expressions.
• The seven basic logic gates includes: AND, OR, XOR, NOT, NAND, NOR, and XNOR.
• The relationship between the input-output binary variables for each gate can be represented in tabular form by a truth table.
• Each gate has one or two binary input variables designated by A and B and one binary output variable designated by x.

AND GATE:

The AND gate is an electronic circuit which gives a high output only if all its inputs are high. The AND operation is represented by a dot (.) sign.

OR GATE:

The OR gate is an electronic circuit which gives a high output if one or more of its inputs are high. The operation performed by an OR gate is represented by a plus (+) sign.

NOT GATE:

The NOT gate is an electronic circuit which produces an inverted version of the input at its output. It is also known as an Inverter.

NAND GATE:

The NOT-AND (NAND) gate which is equal to an AND gate followed by a NOT gate. The NAND gate gives a high output if any of the inputs are low. The NAND gate is represented by a AND gate with a small circle on the output. The small circle represents inversion.

NOR GATE:

The NOT-OR (NOR) gate which is equal to an OR gate followed by a NOT gate. The NOR gate gives a low output if any of the inputs are high. The NOR gate is represented by an OR gate with a small circle on the output. The small circle represents inversion.

Exclusive-OR/ XOR GATE:

The 'Exclusive-OR' gate is a circuit which will give a high output if one of its inputs is high but not both of them. The XOR operation is represented by an encircled plus sign.

EXCLUSIVE-NOR/Equivalence GATE:

The 'Exclusive-NOR' gate is a circuit that does the inverse operation to the XOR gate. It will give a low output if one of its inputs is high but not both of them. The small circle represents inversion.