Electronic Systems

(1)

Electronic Systems

ENGG1015 1^st 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

1st semester, 2010 ENGG1015 - Dr. H. So 2

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

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

•  …

(2)

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 ^PhysicalWorld

•  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

(3)

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

(4)

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

(5)

Input Stage: ADC

Physical World

Digital Systems

ADC DAC

3, 5, 6, 7… 7.2, 6.1, 4.8, 3.14…

Input Process Output

Input Stage: ADC

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.

v_in 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

(6)

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 v_t, 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 v_in to another reference input (v_ref).

vin

v_ref out

v_in 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

v_in

vref out ADC

What are those “1”s and “0”s?

I/O Characteristics of 1-bit ADC

1

0 0 1 0 1 0 1 0

time v_in

v_ref 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 V_cc or V_dd

 Minimum allowable voltage usually is 0 volt (not

“0”).

(7)

Realistic Circuit I/O 1-bit ADC

1

0 0 1 0 1 0 1 0

time v_in

vref

out

0 3.3

Real Circuits

1

0 0 1 0 1 0 1 0

time v_in

vref

out

0 3.3