1. Logic Gates
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2. • Saqib Naveed
sendsaqib@gmail.com
03345813561
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3. •What is Logic??
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Logic
Reasoning conducted or assessed according
to strict principles of validity.
a system or set of principles underlying the
arrangements of elements in a computer or
electronic device so as to perform a
specified task.

6. Logic Gates.
Logic gates are electronic circuits that
operate on one or more input signals to
produce an OUtput signal.

7. Boolean algebra is the algebra of two values. These
are usually taken to be 0 and 1, as we shall do here,
although F and T, false and true, etc. are also in
common use.

8. Basic logic gates
• Not
• And
• Or
• Nand
• Nor
• Xor
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9. Truth Table
A truth table is a mathematical table used in logic—
specifically in connection with Boolean algebra, boolean
functions, and propositional calculus—to compute the
functional values of logical expressions on each of their
functional arguments, that is, on each combination of values
taken by their logical variables ...

10. A
a A
0 1
1 0
Truth Table:
A
The output A is true when the input a is NOT true, the output is the inverse of
the input: a = NOT A
A NOT gate can only have one input. A NOT gate is also called an inverter.
NOT

11. AND
A
B
A*B
Logic Gate:
Series Circuit:
A B
AA BB A*BA*B
00 00 00
00 11 00
11 00 00
11 11 11
Truth Table:A*B
"If A AND B are both 1, then Q should be 1.“
(All or nothing.)

12. Three Input AND Gate
A B C ABC
0 0 0 0
0 0 1 0
0 1 0 0
0 1 1 0
1 0 0 0
1 0 1 0
1 1 0 0
1 1 1 1

13. A
B
A+B
Logic Gate:
Parallel Circuit:
A
B
AA BB A+BA+B
00 00 00
00 11 11
11 00 11
11 11 11
Truth Table:A+B
OR
"If A is 1 OR B is 1 (or both are 1), then Q is 1."

14. • Find the output of the following circuit
• Answer: (x+y)y
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x+y
y
(x+y)y
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15. • Because + and * are binary operations, they
can be cascaded together to OR or AND
multiple inputs.
A
B
C
A
B
C
A+B+C
A+B+C
A
B
A
B
C
ABC
ABC

16. NAND and NOR Gates
• NAND and NOR gates can greatly simplify circuit diagrams.
NAND inverts the output of AND.
• NOR inverts the output of OR.
NAND
NOR
AA BB AA↑↑BB
00 00 11
00 11 11
11 00 11
11 11 00
AA BB AA↓↓BB
00 00 11
00 11 00
11 00 00
11 11 00

17. XOR and XNOR Gates
XOR
XNOR
AA BB AA⊕⊕BB
00 00 00
00 11 11
11 00 11
11 11 00
A B A B
0 0 1
0 1 0
1 0 0
1 1 1
XOR (exclusive OR) :"If either A OR B is 1, but NOT both, Q is 1."
XNOR (exclusive NOR) : invert output of XOR

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