2. 28-Jul-19 2
Prepared For
SN Name ID No Program
01 Rihab Rahman CONFIDENTIAL BCSE
02 Rakib Uddin CONFIDENTIAL BCSE
03 Saifullah Al Mamun CONFIDENTIAL BCSE
04 Tufail Ahmed CONFIDENTIAL BCSE
05 Shuvo Saha CONFIDENTIAL BCSE
Prepared By
4. 28-Jul-19 4
Combinational Logic Circuit
The combinational logic circuits in digital circuit theory can
be defined as a type of digital logic circuit implemented using
Boolean circuits, where the output of logic circuit is a pure
function of the present inputs only.
Rihab Rahman
5. 28-Jul-19 5
Adder
A combinational logic circuit that perform addition between
two or more bits and produces sum and carry is called adder.
There are two types of adder. They are -
❖Half Adder
❖Full Adder
Rihab Rahman
6. 28-Jul-19 6
Half Adder
A combinational logic circuit that perform addition between
two bits and produces carry and sum is called half adder.
S = A⊕B = A’B + AB’
C = A.B
Rihab Rahman
7. 28-Jul-19 7
Full Adder
A combinational logic circuit that perform addition between
three bits and produces carry and sum is called full adder.
Fig: Block Diagram of Full Adder
Rihab Rahman
9. 28-Jul-19 9
Subtractor
A combinational logic circuit that perform subtraction
between two or more bits and produces difference and
borrow is called subtractor. There are two types of
subtractor. They are -
❖Half Subtractor
❖Full Subtractor
Tufail Ahmed
10. 28-Jul-19 10
Half Subtractor
A CL circuit that perform subtraction between two bits and
produces difference and borrow is called half subtractor.
D = A ⊕ B
Bo = A’B Tufail Ahmed
11. 28-Jul-19 11
Full Subtractor
A CL circuit that perform subtraction between two bits,
taking into account that a 1 may have been borrowed by a
lower significant stage and produces difference and borrow
is called half subtractor.
Fig: Block Diagram of Full Subtractor
Tufail Ahmed
13. 28-Jul-19 13
Universal Gate
A universal gate is a gate which can implement any Boolean
function without need to use any other gate type. The NAND
and NOR gates are universal gates. They can perform as like
as the basic gates.
Rakib Uddin
16. 28-Jul-19 16
NAND Gate - Invert OR
Applying DeMorgan's Law: Invert-OR = NAND
This NAND symbol is called Invert-OR. Since inputs are
inverted and then ORed together. AND-Invert & Invert-OR
both represent NAND gate
Saifullah Al Mamun
17. 28-Jul-19 17
NOR Gate – Invert AND
The Invert-AND symbol is also used for NOR
This NOR symbol is called Invert-AND, since inputs are
inverted and then ANDed together. OR-Invert & Invert-
AND both represent NOR gate.
Saifullah Al Mamun
18. 28-Jul-19 18
XOR Implementation
The XOR gate is a digital logic gate that gives a true (1 or
HIGH) output when the number of true inputs is odd. If both
inputs are false (0/LOW) or both are true, a false output
results.
Fig: XOR Implementation by NAND
Saifullah Al Mamun