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
H
L time
1 semester
ENGG1015:
Hybrid
Today
Course Topics
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
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
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
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
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
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
Subsystem A
Subsys Subsys C
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
Top-Level System Subsys B Subsystem A
Subsys Subsys C
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
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
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
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
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
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.
Digital Processing Systems
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
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?
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?
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
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
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
Input Stage: ADC
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
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
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.
vin ADC 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
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).
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 vin ADC 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
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”?
Logic Families
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”).
Realistic Circuit I/O 1-bit ADC
1
0 0 1 0 1 0 1 0
time vin
vref out
0 3.3
Real Circuits
1
0 0 1 0 1 0 1 0
time vin
vref out
0 3.3
