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Electronic Systems
ENGG1015
1st Semester, 2010
Dr. Hayden Kwok-Hay So
Department of Electrical and Electronic Engineering
Introduction
Recall that ENGG1015 is about a hybrid top-down introduction to EEE
Today: A brief detour to the bottom
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H
L time
1 semester
ENGG1015: Hybrid Today
Course Topics
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Applications
Systems
Digital Logic
Circuits
Electrical Signals
High Level
Low Level
• Computer & Embedded Systems • Computer Network • Mobile Network
• Image & Video Processing
• Combinational Logic • Boolean Algebra
• Basic Circuit Theory
• Voltage, Current • Power & Energy
Today
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Electronic Systems
All electronic/electrical systems must ultimately be dealing with the physical world: • Temperature of the air, • Time, • Light, • Sound, • Human movement…
Hierarchy (the use of sub-system), might hide that fact, but the all systems do interact with the physical world
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Process Output Input Physical World
Physical World
System Components - Input
Convert physical quantities into internal quantities that are easy to manage
In EEE, it usually means converting a physical quantity into electrical signals, such as voltage (V), current (I), resistance (R), etc…
Examples • A microphone translates movement of air in the form of air
pressure into voltage • A light sensor translate light intensity (lumens) into
resistance • A thermistor translates temperature into resistance
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Input Physical World
• Voltage (V) • Current (I) • Resistance (R) • Capacitance, Inductance…
• Sound • Temperature • Light • Pressure • …
System Components - Output
Convert internal quantities that are easy to manage into physical quantities that interact with the physical world
Examples • A speaker translates voltage values (V) into movement
of air in the form of air pressure that generate sound • A light bulb that turns current values (I) into light • A motor that drives a wheel to spin • A solenoid that generates a pulling force on a shaft
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Output Physical World
• Voltage (V) • Current (I) • Resistance (R) • Capacitance, Inductance…
• Sound • Temperature • Light • Pressure • …
System Components - Processing
Performs the intended function of the system. Examples
• Amplifies the electrical signal from a microphone • Control the power of the motor of a fan depending on
input voltage Slightly more complex example:
• Mixes the voltage input from two different microphones, amplifies the signal, and control the voltage that will drive a signal indicator and output speaker
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Process
Top-Level System Subsys B
Complex Systems (1)
Decompose a system into multiple sub-systems • Each sub-systems can be decomposed into more sub-
systems • A top-down approach
Compose larger systems by connecting smaller sub-systems • Each composed system can be used to compose even
bigger systems • A bottom-up approach
The organization of sub-systems form a hierarchy
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Subsystem A Subsys
C Subsys B-2
Subsys B-1
Complex Systems (2)
Engineers usually represent each sub-system as a block, forming block diagrams.
The boundary of each sub-system is somewhat arbitrary • Up to the engineering team
But the key is to have a clean and well-defined interface
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Top-Level System Subsys B Subsystem A
Subsys C Subsys
B-2
Subsys B-1
Analog and Digital
In electronic systems, the processing and transfer of a signal can broadly classified as analog or digital in nature. • Possible to mix-and-match
An analog system processes signals with continuous values • e.g. Temperature is now 23.132948123… °C
A digital system processes signals with discrete values • e.g. The time now is 9:32am, temperature is 24 °C
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Analog Systems An analog electronic system processes
signals with continuous values
Usually processes in continuous time as well • Some sub-systems work with continuous
values in discrete time
The exact value of the signal matters
No approximation needed
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Analog Systems - Pros
Most physical quantities are continuous in nature: • e.g. temperature, time, humidity, pressure
The fundamental electronic quantities are also continuous in nature: • Voltage, Current, Resistance
Analog processing is the most “natural” way of processing information from the physical world
Fastest way to process any signal
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Output Process
V V
sound wave Sound wave
Analog Systems - Cons Since exact value of a signal is needed, any
degradation of signal will be reflected at the output. Examples: Interference, sometimes called noise, from outside
the system: • Radio frequency interference (RFI)
Noise within the system: • Electric component’s behavior changes due to
temperature change • Thermo noise in circuits
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 – Cons (cont’d) Very difficult to store any exact value, in
continuous time Difficult to process signals based on previous
values • Echo cancellation • Reverb
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…
Note: it is difficult, not impossible in above
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Digital Systems A digital electronic system processes signals
with discrete values in discrete time 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 25 °C • The process of obtaining data at discrete time or
space is called sampling. • More on sampling & quantization later
The continuous values of the input signals represented by a series of finite number of discrete values.
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Digital Processing Systems
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Process Output Input Physical World
Physical World
Analog Systems
Digital Systems ADC DAC
3, 5, 6, 7… 7.2, 6.1, 4.8, 3.14…
Digital Systems – Pros Discrete values are easy to store, transport
• No degradation over time & space Easy to process “back-in-time”
• Knowing the past make predicting the future a lot easier
Enable very powerful and complicated processing of input • e.g. complex logic, encryption, compression, etc
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 The actual value of the physical
phenomenon is lost • Garbage in garbage out
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.
Q: Do you loose the information between sampling point?
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Quick Summary Quiz Consider an analog and a digital
system, which of them is better in: • processing the exact value of a physical
phenomenon? • processing the exact value of a physical
phenomenon 1 day after the phenomenon has happened?
• producing the exact same result in two different occasions?
Which one is better?
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Tutorials Tutorials will start next Monday and will
repeat on Wednesday with same content
You may attend either class A or class B’s tutorial session
First tutorial’s topic: review on circuits • Extremely useful for your project
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Pre-Project Lab 2-4 pm Monday to Friday @ LG205
CYC building Starts next week Compulsory Graded Mon, Wed, Thu, Fri: 36 students per
session Tue: 20 students per session
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Pre-Project Lab Signup Need to sign up for the lab session that you intend
to join Signup link active starting 1pm Friday, Sep 10 for
24 hours • Will be posted on course website
Optional group signup • If you have already found your partners for project,
signup to the SAME session Project group will be formed within the lab session Need login/password from EEE CSG for signup
• If you have not received it already, send email to [email protected]
• Or visit Rm 804, CYC building
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Input Stage: ADC
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Physical World
Physical World
Digital Systems
ADC DAC
3, 5, 6, 7… 7.2, 6.1, 4.8, 3.14…
Input Process Output
Input Process Output
Input Stage: ADC
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Physical World
Physical World
Digital Systems
ADC DAC
3, 5, 6, 7… 7.2, 6.1, 4.8, 3.14…
Process Output Input
ADC
Analog to Digital Conversion The process of converting analog
information into digital representation is referred as analog to digital conversion • The circuit that performs the conversion is
called an analog to digital convertor (ADC). The reverse process is called digital to
analog conversion, using a digital to analog convertor (DAC).
Today: We’ll look at how to build a 1-bit ADC circuit • Review of basic circuit design • Extremely useful for project
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1-bit ADC
Recall that an ADC converts (quantizes) an analog signal into digital representation
An 1-bit ADC quantizes the analog input into a two possible outcomes • hot VS cold • analog signal is presented VS not presented • input voltage is higher than certain value VS otherwise. • …
Use a single binary bit to represent 2 values In other word, an 1-bit ADC makes a binary decision about
the analog input.
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ADC vin out
1-bit ADC: logical design Essentially, an 1-bit ADC is a
comparator • Compares to a built in threshold • Compares to a outside input value
An electronic ADC implements this concept using electronic circuits
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1-bit ADC (cont’d)
In the simplest case, an 1-bit ADC can be thought as a thresholding circuit, • If the input voltage is higher than a built-in threshold vt,
then the output is “1”, otherwise the output is “0”. In a slightly more elaborated design, an 1-bit ADC
can be implemented as a comparator circuit that compares the value of the ADC input vin to another reference input (vref).
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vin vref
out vin out
out = “1” if vin > vt out = “1” if vin > vref
Threshold Comparator
Peeling an ADC onion
Note that what we have done so far was indeed gradually unveiling the inner details of an ADC
From the abstract concept of analog-to-digital conversion, we are moving downward to unveil more implementation details with the underlying circuits • A thresholding or comparator circuit
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ADC vin out 1 layer down
vin vref
out
ADC
What are those “1”s and “0”s? Next:
“1” or “0” “1” or “0”
I/O Characteristics of 1-bit ADC
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1 0 0 1 0 1 0 1 0
time
vin
vref
out
Implementing Logic Levels The “0”s and “1”s in previous slides are merely
symbols to represent two logical states • e.g. the value 1/0, high/low, on/off, true/false, hot/
cold…
In actual circuit implementations, these “0”s and “1”s are represented by the voltage (potential) presented at the output. • NOTE: There are other circuit implementations
that uses current at the output node to represent “0”s and “1”s, but we will focus in voltage here.
What voltage should be used to represent “1” and what voltage to represent “0”?
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Logic Families
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Image source: http://www.interfacebus.com/voltage_LV_threshold.html
There are industrial standards on the voltage levels for representing logic levels in discrete components.
Sometimes referred as I/O standards.
Own standard? You can have your “own standard” when you
build your own circuit, e.g.: • digital VLSI designs
• e.g. 3.3V, 2.5V, 1.5V, 1.2V… • Your class project
• e.g. 12V
Usually uses the maximum allowable voltage as “1”, and minimum allowable voltage as “0”
Customary to label the max voltage as Vcc or Vdd
Minimum allowable voltage usually is 0 volt (not “0”).
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Realistic Circuit I/O 1-bit ADC
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1 0 0 1 0 1 0 1 0
time
vin
vref
out
0
3.3
Real Circuits
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1 0 0 1 0 1 0 1 0
time
vin
vref
out
0
3.3