small description of digital gates of digital electronics

1. DIGITAL
ELECTRONICS
PRESENTED BY :
LATA KUSHWAHA

2. INTRODUCTION
• Digital Electronics
• Why needed ?
• Difference between analog and digital electronics
• Important topics covered in digital electronics
• Logic Gates
• Boolean Algebra
• Integrated Circuit

3. Digital Electronics
That branch of electronics which deals with the
digital signals to perform various tasks and
meet various requirements.
Uses only binary digits 0 and 1.

4. Why needed ?
• Most analog systems were less accurate and
were slow in computation and performance.
• Ability to work faster.
• Can be operate on very high frequency.
• Much economical than analog methodology.

5. Difference
Analog Electronics Digital Electronics
1. Usually larger circuits and occupies
more area.
1. Has smaller IC and occupies lesser
area.
2. Its measuring instruments are less
accurate , chance of misreading are
more.
2. Its measuring instruments are more
accurate and there are no case
misreading it.
3. Higher harms in case of drops and falls. 3. Lesser harms on drops and falls.

6. Some important topics
• Logic Gates
• Boolean Algebra
• Integrated Circuit

7. LOGIC GATES
• Logic gates are the basic blocks of the digital
circuits.
• Circuits which are used to process digital signals
are called logic gates.
• It is of two types:
- Combinational Gates
- Sequential Gates

8. Combinational Gates
•The output at any instant depends upon the inputs at that
instant.
•Means previous input does not have any effect on the output.
• Combinational gates are further divided into given
categories :
- Basic gates: OR , NOT and AND
-Two universal gates: NAND , NOR.
-Arithmetic Gates: XOR , XNOR,

9. Basic Gate : AND
Symbol Truth Table
Using diode Using Transistor

10. OR Gate
symbol Truth Table
Using diode Using Transistor

11. NOT Gate
Symbol Truth Table
Using diode Using Transistor

12. Universal Gate: NAND
Symbol Truth Table
2-input NAND Gate
B A Q
0 0 1
0 1 1
1 0 1
1 1 0
Boolean Expression Q = A.B Read as A AND B gives NOT Q

13. NOR Gate
Symbol Truth Table
Circuit Diagram Using Transistor

14. Arithmetic Gate: XOR
Symbol Truth Table
Logic Circuit Diagram:

15. XNOR
Symbol Truth Table
Logic Circuit Diagram:

16. Adder
• An adder is a digital circuit that performs addition of
numbers.
• It produces sum and carry.
• Adders are classified into two types:
- Half adder
- Full adder
• The relationship between the Full-Adder and the Half-
Adder is half adder produces results and full adder uses half
adder to produce some other result.

17. Half Adder
• A logic circuit that adds two bits producing a sum and carry to be used in the next
higher position is called Half Adder.
• By using half adder, we can design simple addition with the help of logic gates.
Logic Circuit Diagram: Truth Table :

18. Full Adder
• A logic circuit that adds three bits producing a sum and a carry bit from previous
addition, which results in a sum and carry is called Full Adder.
• The first two inputs are A and B and the third input is an input carry as C-IN.
Logic Circuit Diagram: Truth Table :

19. Subtractor
• An subtractor is a digital circuit that performs
addition of numbers.
• It produces difference and borrow.
• Subtractors are classified into two types:
- Half Subtractor
- Full Subtractor

20. Half -Subtractor
• It is a logic circuit which subtracts two bits and produces their difference.
• Consists of one XOR and one AND gate.
• There are two inputs and two outputs one difference and other borrow.
Logic Circuit Diagram: Truth Table :
Expression:
• D = (X’Y + XY’) = X ⊕ Y
• B = X’Y

21. Full Subtractor
• Full subtractor as a combinational circuit which takes three inputs and produces two
outputs difference and borrow.
• Can be designed with the help of two half subtractors and an OR gate.
Logic Circuit Diagram: Truth Table :
Expression :
• (X’Y’Z + X’YZ’ + XY’Z’ + XYZ) = X ⊕ Y ⊕ Z
• (X’Y’Z + X’YZ’ + X’YZ + XYZ) = X'(Y ⊕ Z) + YZ

22. Sequential Logic Gates
• A sequential logic circuit is one whose outputs depend not only on its current
inputs, but also on the past sequence of inputs.
• It possess a memory function.
• Their output depends on a SEQUENCE of the events occurring at the circuit
inputs.

23. BOOLEAN ALGEBRA
• Boolean algebra is the symbolic logic invented by Boole for analysis and design of
digital circuits.
• Only three operations are possible in Boolean algebra which are as follows:
- the OR addition
- the AND multiplication
- the NOT operation
• De-morgan’s theorem is also applied in this:
(i). (ii).
Expression:

24. INTEGRATED CIRCUIT
• An IC or monolithic integrated circuit is a set of electronic
circuit on one small flat piece of semiconductor material
normally silicon.
• Hundreds of integrated circuits are made at the same time
on a single, thin slice of silicon and are then cut apart into
individual IC chips.

25. Thank you