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Digital System & Digital Design

What is System?
Machine: A machine is a tool containing one or more parts that uses energy to perform an intended action.

Machines are usually powered by mechanical, chemical, thermal, or electrical means, and are often motorized.

Historically, a power tool also required moving parts to classify as a machine.


A set of detailed methods, procedures and routines created to carry out a specific activity, perform a duty, or solve a problem.

An organized, purposeful structure that consists of interrelated and interdependent elements (components, entities, factors, members, parts etc.).

These elements continually influence one another (directly or indirectly) to maintain their activity and the existence of the system, in order to achieve the goal of the system.

System Classification
System can be classified in so many ways:

Type of Energy used: Mechanical, Electrical, Electronics, etc…

Size: Mega, mini, Micro

Liner and Non-liner Systems

Time Variant and Time Invariant Systems

Liner Time variant and Liner Time invariant systems

Static and Dynamic Systems

Causal and Non-causal Systems

Invertible and Non-Invertible Systems

Stable and Unstable Systems

Analog and Digital Systems

Control System
Open loop

Closed loop: Feedback

Analog Vs Digital System
Open loop




Analog signal is a continuous signal which represents physical measurements.

Digital signals are discrete time signals generated by digital modulation.


Denoted by sine waves

Denoted by square waves


Uses continuous range of values to represent information

Uses discrete or discontinuous values to represent information


Analog technology records waveforms as they are.

Samples analog waveforms into a limited set of numbers and records them.

Data transmissions

Subjected to deterioration by noise during transmission and write/read cycle.

Can be noise-immune without deterioration during transmission and write/read cycle.

Response to Noise

More likely to get affected reducing accuracy

Less affected since noise response are analog in nature


Analog hardware is not flexible.

Digital hardware is flexible in implementation.


Can be used in analog devices only. Best suited for audio and video transmission.

Best suited for Computing and digital electronics.





Analog signal processing can be done in real time and consumes less bandwidth.

There is no guarantee that digital signal processing can be done in real time and consumes more bandwidth to carry out the same information.


Stored in the form of wave signal

Stored in the form of binary bit


Analog instrument draws large power

Digital instrument draw only negligible power


Low cost and portable

Cost is high and not easily portable



High order of 100 megaohm


Analog instruments usually have a scale which is cramped at lower end and give considerable observational errors.

Digital instruments are free from observational errors like parallax and approximation errors.


Human voice in air, analog electronic devices.

Computers, CDs, DVDs, and other digital electronic devices.


Why Digital?
Advantages of Digital –

Disadvantages of Digital –

○ Ease of programmability / manipulate
○ High Speed
○ More reliable
○ Design is easy as its flexible
○ Compatibility with other digital systems
○ Only digitised information can be transported through a noisy channel without degradation
○ Integrated networks
○ Reduction in cost of hardware so less expensive
○ Results can be reproduced easily
○ Information storage can be easier in digital computer systems than in analog ones.

○ Use more energy than analog circuits to accomplish the same tasks, thus producing more heat as well.
○ Digital circuits are often fragile, in that if a single piece of digital data is lost or misinterpreted the meaning of large blocks of related data can completely change.
○ Digital computer manipulates discrete elements of information by means of a binary code.
○ Quantization error during analog signal sampling.
○ Digital communications require greater bandwidth than analogue to transmit the same information.
○ The detection of digital signals requires the communications system to be synchronised, whereas generally speaking this is not the case with analogue systems.

How to design Digital System?
Discrete Chips
Prototype using FPGA
Application Specific Integrated Circuit (ASIC)

Digital Design Fundamentals

Digital Signals
○ Digital Signal is a signal that represents a sequence of discrete values.
○ A logic signal is a digital signal with only two possible values, and describes an arbitrary bit stream.
○ Other types of digital signals can represent three-valued logic or higher valued logics.
○ Digital signals are represented by Binary Number.

Binary Signal
○ Binary (or "base-2") a numeric system that only uses two digits — 0 and 1.
○ Computers operate in binary, meaning they store data and perform calculations using only zeros and ones.
○ While a single binary digit can be used to represent True (1) or False (0) in Boolean logic, multiple binary digits can be used to store large numbers and perform complex functions.
○ In fact, any number can be represented in binary.

Electronics and Switches

○ Electronic switches are the basis of binary digital circuits

○ A switch has three parts
  ●Source Input,
     - Sink Output
     Current wants to flow from source input to output
  ●Control input
     - Voltage that controls whether that current can flow

○ CMOS transistor
  ●Basic switch in modern ICs

Boolean Logic Gates

○ Building Blocks for Digital Circuits
  ●Because Switches are Hard to Work With

○ "Logic gates" are better digital circuit building blocks than switches (transistors)

Boolean Algebra & its Relation to Digital Circuits

○ Boolean Algebra
  ●Variables represent 0 or 1 only
  ●Operators return 0 or 1 only
  ●Basic operators
    - AND: a AND b returns 1 only when both a=1 and b=1
    - OR: a OR b returns 1 if either (or both) a=1 or b=1
    - NOT: NOT a returns the opposite of a (1 if a=0, 0 if a=1)

Converting to Boolean Equations

Q1. a is 1 and b is 1.

Answer: F = a AND b

Q2. either of a or b is 1.

Answer: F = a OR b


Q3. both a and b are not 0.


  (a) Option 1: F = NOT(a) AND NOT(b)

  (b) Option 2: F = a OR b

Relating Boolean Algebra to Digital Design

Implement Boolean operators using transistors

Call those implementations logic gates.

NOT/OR/AND Logic Gate Timing