Digital System Design

ELEC3342

Dr. Hayden Kwok-Hay So

Department of Electrical and

Electronic Engineering

Introduction

What ELEC3342 is about?

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Digital System Design

Digital, not analog

Large, complex, with many

connecting components

Making engineering tradeoff;

Make it beautiful!

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A digital system is an electronic system that

operates based on the digital abstraction.

… As opposed to an analog system…

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Digital Discrete Values

Analog Continuous Values

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è

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n Quantities in the physical world occur mostly as continuous analog values:• Temperature, force, mass, speed

n Basic electronic circuit elements also based on continuous analog values:• Voltage, current, resistance, capacitance, inductor,

frequency of oscillators…

n Building systems that operates with an analog system is somewhat natural…

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In the beginning… All Analog

Analog Systemsn An analog electronic system processes signals

with continuous values

n Usually processes in continuous time as well• Some sub-systems work with continuous values in

discrete time

n The exact value of the signal matters

n No approximation needed

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but very challenging…

Analog Systems - Challengesn Since exact value of a signal is needed,

any degradation of signal will be reflected at the output.

Examples:

n Interference, sometimes called noise, from outside the system:• Radio frequency interference (RFI)

n Noise within the system:• Electric component’s behavior changes due to

temperature change

• Thermo noise in circuits

n Non-ideal electronic components• A resistor’s true value is never what it is

designed

• Degradation of components over time

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Analog Systems – Challengesn Very difficult to store any exact value, in

continuous time

n Difficult to process signals based on previous values• Echo cancellation

• Reverb

n Difficult to transport signals because signals degrades over any medium of transfer, especially in long distances• Old TV systems suffer from “ghost images”

• Radio station not received well…

n Note: it is difficult, not impossible in above

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Digital Systemsn A digital electronic system processes signals with

discrete values in discrete time

n The exact values of the input signal at discrete point in time are quantized into discrete values• e.g. all values are stored as integers only

• 24.5990010101 °C à 25 °C

• The process of obtaining data at discrete time or space is called sampling.

n The continuous values of the input signals represented by a series of finite number of discrete values.

n Signal processing engineers call this sequence of values … a Signal

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Digital Systems – Pros n Discrete values are easy to store, transport

• No degradation over time & space

n Easy to process “back-in-time”• Knowing the past make predicting the future a lot

easier

n Enable very powerful and complicated processing of input• e.g. complex logic, encryption, compression, etc

n Immune to a lot more interferences from inside and outside of the system than an analog system• E.g. RFI, circuit noise, non-idealistic circuits and

degradation over time• Note: you can still interfere a digital system with

enough power

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Digital Systems – Cons

n The actual value of the physical phenomenon

is lost

• Garbage in garbage out

n Relatively slower than analog systems in

standard circuit implementations

• Competing with speed-of-light in analog systems

• Recall electricity is an effect of electro-magnetic

wave, which travels at speed of light.

n Loss of information between sampled data?

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Digital Processing Systems

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Process OutputInputPhysical

World

Physical

World

Analog

Systems

Digital

Systems ADC DAC

3, 5, 6, 7… 7.2, 6.1, 4.8, 3.14…

Analog to Digital Converter Digital to Analog Converter

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time

data

valu

es

continuous discrete

continuous

dis

cre

te

Electronic

circuitsSample-and-hold

circuits in ADCs

Combinational

Logic

Sequential

Logic

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(Binary) Digital Abstractionn Abstract all signals as TWO discrete values

• Usually denoted TRUE, FALSE, high, low, ‘1’, ‘0’• We use TRUE, high, ‘1’ synonymously

n The value TRUE does not necessarily correspond to a high physical voltage• We can define TRUE anyway we want as long as it

does not overlap with that of FALSE

• More in later lectures…

n Binary system can be effectively analyzed with Boolean algebra• Allows easy logic manipulation in the system• Provides a mathematical basis for modeling the

behavior of the system

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ELEC3342 Administrivia

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Dr. Hayden SoInstructors

TA Mr. Yizhao GAO

Lectures

http://www.eee.hku.hk/~elec3342

Mo 12:30-2:20pm MB167

Th 12:30-1:20pm MB167

TutorialsNo Scheduled time. But will arrange

additional office hours for homework

Web

Special Pandemic Arrangementn Primarily face-to-face lectures

n Video of lectures recorded and posted online after lecture• Don’t come to lecture if you are

sick

• Don’t worry if you are still stuck outside HK

n Project requires access to hardware (for hw groups)

n Project can be completed with only simulations (if cannot arrive in HK)

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Textbook

n Reading materials will be drawn from the

following textbook:

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“Digital Design and Computer Architecture”

David Harris Sarah Harris

2nd Edition; Morgan Kaufmann (2012)

ISBN-13: 9780123944245

Assessments

Homework 30% • 3 homework assignments

Project 40% • Multi-part projects

• Project report

• Presentation/Demonstration

Exam 30% Cumulative of entire semester

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Learning Outcome

n Understand the principles and methodologies

of digital logic design at register-transfer level

n Formulate high-level specification of a digital

system and synthesize the specification into a

digital logic network

n Develop a relatively large and complex digital system with modern computer-aided design

(CAD) tools

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focu

s o

f th

is c

ou

rse

programs

device drivers

instructions

registers

datapaths

controllers

adders

memories

AND gates

NOT gates

amplifiers

filters

transistors

diodes

electrons

Agenda of ELEC3342

n Signals in digital systems

n Combinational logic design

n Sequential logic design

n VHDL

n Finite State Machine design

n Memory

n Arithmetic circuits

n Input/Output

n High-speed design

n Power and clock signal design

n FPGA and its applications

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Morse Code Decoder

n Implemented using VHDL

n Design & test in software

n Run on real hardware

n Group project from 1-4

person (more details later)

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Your

Design

Hardware

n Digilent Basys3

• Xilinx Artix-7 FPGA (XC7A35T-

1CPG236C)

n Board be distributed on demand

(only if you have had good

progress in previous parts)

n 1 board per group

n Return board in good working

condition toward the end of

semester

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Microphone input

Software

n Xilinx Vivado Design Suite

• Industrial software for Xilinx FPGA

n Download and install free version

• Xilinx calls it “Webpack version”

• Runs on Windows and Linux

n (Use VirtualBox + Linux on OSX)

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In Conclusion…

n Digital systems process and transmit values

based on the digital abstraction.

n Operating on discrete values facilitate

building and analyzing very complex systems

n All modern digital systems operate on binary

values

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