Lec1 - Analog and Digital systems

FacultyofEngineering-UCP
IntroductiontoAnalogandDigitalSystems
Intro. to Analog and Digital Systems
Prof. Mohammad Salman Aslam
Faculty of Engineering
University of Central Punjab
Digital Logic & Design (DLD)
Lecture No: 1b – 3rd Semester

2
Basic Definition of Analog System
 An Analog System or quantity is one having continuous values.
A nominal continuous electrical signal that varies in amplitude or
frequency in response to changes in sound, light, heat, position or pressure
is called analog signal and the system based on this type of signal is called
Analog System.
OR
 An Analogue quantity is one having a continuous set of values.
OR
 In an analog system, the quantities can vary over a continuous range
of values. Most things that can be measured quantitatively appear in
nature in analog form.

3
 We live in an analog world (continuous)
 Analog signals are continuous in nature
• Smooth transition over a period of time
• Represent a physical quantity or phenomenon
• e.g. temperature of a cup of tea being boiled
Basic Definition of Analog System (Cont.)

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Representation of Analog System

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Representation of Analog System

6
Basic Definition of Digital System
 A circuit designed to respond at input voltages at one of a finite number of
levels and, similarly to produce output of a finite number of levels is
called digital system. And a digital quantity is one having a discrete set of
values.
OR
 A digital quantity is one having a discrete set of values. In these systems
the values are not defined at every point rather on discrete points.
OR
 A Digital quantity is one having a discrete set of values. A Digital
quantity is often a sampled analogue quantity.
 Examples of Digital Systems are Digital Computers; Digital Telephone
switching exchanges, Digital voltmeter, Frequency counter,
Calculators etc.

7
Representation of Digital System

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Representation of Digital System

9
Advantages of Digital System
 An increasing majority of applications in electronics as well as in most
other technologies use digital techniques to perform operations that
were once preformed using analog methods. The main reasons to use
the digital technology are:
 Digital system is generally easier to design.
 Information storage is easier in Digital Systems.
 Accuracy and precision are greater.
 Operation can be easily programmed.
 Digital circuits are less affected by noise.

10
Disadvantage of Digital System
 There is really only one major drawback when using
Digital System techniques:
 The real world is mainly Analog.
 Most physical quantities are Analog in nature, and it is
these quantities that are often the inputs and outputs that
are being monitored, operated on, and controlled by a
system.

11
Process of Conversion from a Analog-to-Digital
(ADC) and Digital to Analog (DAC) Signal
To take advantage of digital techniques when dealing with analog
inputs and outputs, three steps must be followed:
1. Convert the real-world analog inputs to digital form. (ADC)
2. Process (operate on) the digital information.
3. Convert the digital outputs back to real-world analog form. (DAC)
The following diagram shows a temperature control system that requires
analog/digital conversions in order to allow the use of digital processing
techniques.

12
Process of Conversion from a Analog-to-Digital
(ADC) and Digital to Analog (DAC) Signal
Digitization (Why?)
 Process of conversion from analog to digital is called digitization
 Analog to digital (ADC) converters perform digitization
 Digital to analog (DAC) converters regenerate the analog signals
from their digitized form
 The world around us is analog
 Digital systems are simple to understand & comprehend
 Thus common practice is to convert analog signals into digital signals
form for efficient processing of signals
 Inevitable to avoid loss of some accuracy (information) due to this
conversion
 Reason: digital systems can only represent fixed (finite or discrete) set
of values

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Digitization Example (Converting
Analog signal into Digital)

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Signal representation (Voltage)
 Computers use low power supply voltage, typically from
0V to 5V
 In decimal numbering system, the voltage levels are
divided into 10 equal parts. Therefore:
• 0 represents 0 – 0.5V
• 1 represents 0.5 – 1.0V
• 2 represents 1.0-1.5V and so forth.
 Only 0.5V separate two consecutive voltage ranges if
decimal digits are used.
Binary 1: Any voltage between 2V to 5V
Binary 0: Any voltage between 0V to 0.8V

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Representing Binary Quantities in Digital
We can see another significant difference between
digital and analog systems. In digital systems, the exact
value of a voltage is not important; e.g., a voltage of
3.6V means the same as a voltage of 4.3V. In analog
systems, the exact value of a voltage is important.

16
Signal representation (Voltage)

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Representing Binary Quantities
 A binary number, at its most basic level, is called a BIT
(BIT being short for Binary-digIT). A BIT is a value which can
hold two possible states. These states can be many different things.
They can be...
»TRUE or FALSE
»ON or OFF
»YES or NO
»UP or DOWN
»ACTIVE or INACTIVE
 Numerically they are expressed as ONE (1) or ZERO (0).
Every piece of information stored in a computer system
ultimately breaks down to one of these two BITS.

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 ICs are classified by the complexity of the silicon chip that they contain.
The classification is decided by determining the number of gate circuits
contained in the chip.
 SSI – Small-Scale Integration : 1 → 10 gates.
For example, basic gates and flip-flops.
 MSI – Medium-Scale Integration : 10 → 100 gates.
For example, encoders, decoders, counters, registers,
multiplexers, arithmetic circuits, small memories and others.
 LSI – Large-Scale Integration : 100 → 10,000 gates.
For example, memories and simple microprocessors.
 VLSI – Very Large-Scale Integration : 10,000 → 99,999
gates. For example, microprocessors.
 ULSI – Ultra Large-Scale Integration : 100,000 + gates.
For example, PC 3D graphics cards microprocessor controllers
and microprocessors.
Integrated Circuit Complexity Classifications

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Integrated Circuit (Layout)
SRAM
SRAM
Data paths
Standard cells

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Development of IC’s in terms of Size
0.8 mm 0.6 mm 0.5 mm 0.35 mm 0.25 mm 0.18 mm 0.1 mm
1 mm
1990 1992 1994 1995 2000 2003 2006 2010
Submicron Deep Submicron
Nanometer

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