Unit 3
Logic Gates and Boolean Algebra
Logic gates
• Logic gates are electronic circuits that operate on one
or more input signals to produce standard output
signal
• These are the building blocks of all the circuits in a
computer
• Logic gates are used in microprocessors,
microcontrollers, embedded system applications, and
in electronic and electrical project circuits.
• The basic logic gates are categorized into seven:
AND, OR, XOR, NAND, NOR, XNOR, and NOT.
Types of Logic Gates
AND Gate
• The AND gate is a digital logic gate with ‘n’ inputs one
output, which performs logical conjunction based on
the combinations of its inputs.
• The output of this gate is true only when all the inputs
are true. When one or more inputs of the AND gate’s
inputs are false, then only the output of the AND gate
is false.
AND Gate (Block Diagram and
Truth Table)
OR Gate
• The OR gate is a digital logic gate with ‘n’ inputs
and one output, that performs logical conjunction
based on the combinations of its inputs.
• The output of the OR gate is true only when one or
more inputs are true.
• If all the inputs of the gate are false, then only the
output of the OR gate is false.
OR Gate (Block Diagram and
Truth Table)
NOT Gate
• The NOT gate is a digital logic gate with one input
and one output that operates an inverter operation
of the input.
• The output of the NOT gate is the reverse of the
input.
• When the input of the NOT gate is true then the
output will be false and vice versa.
NOT Gate (Block Diagram and
Truth Table)
NAND Gate
• The NAND gate is a digital logic gate with ‘n’ inputs
and one output, that performs the operation of the
AND gate followed by the operation of the NOT gate.
• NAND gate is designed by combining the AND and
NOT gates.
• If the input of the NAND gate high, then the output
of the gate will be low.
NAND Gate (Block Diagram and
Truth Table)
NOR Gate
• The NOR gate is a digital logic gate with n inputs
and one output, that performs the operation of the
OR gate followed by the NOT gate.
• NOR gate is designed by combining the OR and NOT
gate.
• When any one of the inputs of the NOR gate is true,
then the output of the NOR gate will be false.
NOR Gate (Block Diagram and
Truth Table)
Exclusive-OR Gate
• The Exclusive-OR gate is a digital logic gate with
two inputs and one output.
• The short form of this gate is Ex-OR.
• It performs based on the operation of the OR gate.
• If any one of the inputs of this gate is high, then the
output of the EX-OR gate will be high.
XOR Gate (Block Diagram and
Truth Table)
Expression of XOR gates
Exclusive-NOR Gate
• The Exclusive-NOR gate is a digital logic gate with
two inputs and one output.
• The short form of this gate is Ex-NOR. It performs
based on the operation of the NOR gate.
• When both the inputs of this gate are high, then the
output of the EX-NOR gate will be high. But, if any
one of the inputs is high (but not both), then the
output will be low.
XNOR Gate (Block Diagram and
Truth Table)
Expression of XNOR gate
Summary of Logic gates
• For AND Gate – If both the inputs are high then the
output is also high
• For OR Gate – If a minimum of one input is high then
the output is High
• For XOR Gate – If the minimum one input is high then
only the output is high
• NAND Gate – If the minimum one input is low then the
output is high
• NOR Gate – If both the inputs are low then the output is
high.
