electronic systems - university of hong kongengg1015/fa10/handouts/02-elec...• thermo noise in...

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

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

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

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


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


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.


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


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


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


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

electronic systems - university of hong kongengg1015/fa10/handouts/02-elec...• thermo noise in...

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