This manuscript addresses the need for a subject digital logic design for an undergraduate ICT course.

1. Introduction to Digital Logic Design
Dr. Varun Kumar
Dr. Varun Kumar Introduction 1 / 13

2. Outlines
1 What do we mean by digital ?
2 Need of digital
3 Digital logic
4 Design perspective
5 References
Dr. Varun Kumar Introduction 2 / 13

3. Source of information
Source of information
Text
⇒ SMS
⇒ E-mail, etc
Audio
⇒ Listening a music or telephonic conversation
⇒ Bronchial sound measured by stethoscope, etc
Image
⇒ Pi-chart
⇒ Graph
⇒ Simulation plot
⇒ Remote sensing image, etc
Video
⇒ Watching a movie
⇒ Tele heart surgery, etc
Dr. Varun Kumar Introduction 3 / 13

4. Transducer
⇒ Text, image, audio, and video are the physical world signal.
⇒ Another type of physical world signal are pressure, temperature, flow
of fluid, etc.
Transducer:
It is is device that converts physical world signal into electrical signal.
Signal:
It is a function that vary with certain parameters.
⇒ For understanding the information and communication technology
(ICT), we should be familiar with electrical signal and their types.
Dr. Varun Kumar Introduction 4 / 13

5. Signal and their classification
Classification :
Analog vs digital signal
(a) A signal whose amplitude can take on any value in a continuous range
is an analog signal.
(b) A signal whose amplitude can take on finite number of values is a
digital signal.
Note :
1 Analog is not the synonyms of continuous time signal.
0 0.1 0.2 0.3 0.4 0.5
Time t →
-2
-1
0
1
2
3
x(t)
Analog and continuous time signal
0 10 20 30 40 50
Sammpling index n →
-2
-1
0
1
2
3
x(n)
Analog and discrete time signal
0 0.1 0.2 0.3 0.4 0.5
Time t →
-2
-1
0
1
2
Digital and continuous time signal
0 10 20 30 40 50 60 70 80
Sampling index n →
-2
-1
0
1
2
Digital and discrete time signal
Dr. Varun Kumar Introduction 5 / 13

6. Need of digital
⇒ As per the nature of signal (analog and digital).
⇒ By default all physical signals are analog in nature.
⇒ Digital signal is a man-made signal.
Merit of digital technology
Less requirement of physical space
Noise immunity
Storage
Encryption
Economical and many more
Note: Digital system is a hardware oriented set-up.
Dr. Varun Kumar Introduction 6 / 13

7. Digital system
Digital system
Note: In circuit level implementation, there is requirement of
Transistor
Resistor
Capacitor, etc
Dr. Varun Kumar Introduction 7 / 13

8. Digital logic
Digital logic
Logic : It is a way for solving a problem in a minimal effort.
⇒ Boolean algebra, K-map, etc.
Example: For a general mathematical operation
⇒ Yadd = A + B → (A, B) ∼ (4, 2) → Yadd = 6
⇒ Ysub = A − B → (A, B) ∼ (4, 2) → Ysub = 2
⇒ Ymul = A × B → (A, B) ∼ (4, 2) → Ymul = 8
⇒ Ydiv = A/B → (A, B) ∼ (4, 2) → Ydiv = 2
Note :
1 Machine does not think as a human.
2 It needs a logic program that acts as an interface between human and
machine understanding.
A = 4 → 0100 and B = 2 → 0010 ⇒ Yadd = 6 = 0110
Dr. Varun Kumar Introduction 8 / 13

9. Design perspective
⇒ Logic itself does not play a vital role for end product development.
⇒ There is requirement of hardware unit (transistor, resistor, capacitor)
for successful implementation of digital logic.
⇒ A = 4 → 0100 → A3A2A1A0 and B = 2 → 0010 → B3B2B1B0 ⇒
Yadd = 6 = 0110 → Y3Y2Y1Y0
⇒ Gate level design → AND, OR, NOT, XOR, NAND, NOR, NXOR
⇒ Transistor level design → npn, pnp, MOSFET, etc
Dr. Varun Kumar Introduction 9 / 13

10. Transistor level design
AND gate implementation
Note:
⇒ Other gates can also be formed with the help elementary unit of
digital logic design, i.e, transistor.
⇒ The aim of design is to reduce the number of basic unit without
disrupting the overall performance.
Dr. Varun Kumar Introduction 10 / 13

11. Conclusion
1 This subject addresses the basic of a digital logic design.
2 What are the different logical operation (especially logic gate) ?
3 How can we minimize the number of basic units of digital logic design
?
4 How the power usage of any hardware unit is minimized ?
5 How do we increase the processing speed of any hardware ?
6 What are the different logic family as per the application ?
Dr. Varun Kumar Introduction 11 / 13

12. References
M. M. Mano, “Digital design, prentice hall,” Upper Saddle River, NJ, 2002.
T. L. Floyd, Digital Fundamentals, 10/e. Pearson Education India, 2010.
S. Salivahanan and S. P. Kumar, Digital circuits and design. Vikas Publishing
House, 2003.
J. F. Wakerly, Digital Design: Principles And Practices, 4/E. Pearson Education
India, 2008.
Dr. Varun Kumar Introduction 12 / 13