electronic systems example:electronic systems …engg1015/fa11/handouts/03-exelecsys.pdfelectronic...

Electronic Systems Example:Electronic Systems Example:Thermo Warning Lightg g

ENGG1015

1st Semester, 2011

Dr. Kenneth Kin-Yip Wong

Department of Electrical and Electronic Engineering

Course TopicsCourse TopicsApplicationsHigh • Image & Video Processing

Systems

gLevel

• Computer & Embedded Systems• Computer Networky

Digital

Computer Network• Mobile Network

• Combinational LogicToday gLogic

Combinational Logic• Boolean Algebra

Today

Circuits • Basic Circuit Theory

ElectricalSignals

LowLevel

• Voltage, Current• Power & Energy

1st semester, 2011 ENGG1015 - Dr. K. Wong 2

Input Stage: ADCInput Stage: ADCDigitalg taSystems

PhysicalWorld

PhysicalWorld

Input Process Output

Input Process OutputWorld World

3, 5, 6, 7… 7.2, 6.1, 4.8, 3.14…

ADC DAC


Input Stage: ADCInput Stage: ADCDigitalg taSystems

PhysicalWorld

PhysicalWorld

Process OutputInput

ADCWorld World

3, 5, 6, 7… 7.2, 6.1, 4.8, 3.14…

ADC DAC


Analog to Digital ConversionAnalog to Digital ConversionThe process of converting analog information into digital representation isinformation into digital representation is referred as analog to digital conversion• The circuit that performs the conversion isThe circuit that performs the conversion is

called an analog to digital convertor (ADC).The reverse process is called digital toThe 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 ADC1 bit ADCADCvin out

Recall that an ADC converts (quantizes) an analog signal

ADCvin out

Recall that an ADC converts (quantizes) an analog signal into digital representationAn 1-bit ADC quantizes the analog input into a two possible outcomesoutcomes• 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 valuesUse a single binary bit to represent 2 values In other word, an 1-bit ADC makes a binary decision about the analog input.


1-bit ADC: logical design1 bit ADC: logical designEssentially, an 1-bit ADC is a comparator• Compares to a built in thresholdCompares to a built in threshold• Compares to a outside input value

An electronic ADC implements this concept using electronic circuitsp g


1-bit ADC (cont’d)1 bit ADC (cont d)vin

out = “1” if vin > vt out = “1” if vin > vref

vinvref

outvin out

Threshold Comparator

In the simplest case, an 1-bit ADC can be thought as a thresholding circuit

Threshold Comparator

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 v to anothercompares the value of the ADC input vin to another reference input (vref).


Peeling an ADC onionPeeling an ADC onionADCvin out 1 layer vin out

ADC “1” or “0”“1” or “0”

N h h h d f i d d

ADCvin outdown vref

out

Note that what we have done so far was indeed gradually unveiling the inner details of an ADCF th b t t t f l t di it lFrom the abstract concept of analog-to-digital conversion, we are moving downward to unveil more implementation details with the underlyingmore implementation details with the underlying circuits• A thresholding or comparator circuit

What are those “1”s and “0”s?Next:


I/O Characteristics of 1-bit ADCI/O Characteristics of 1 bit ADC10 0 1 0 1 0 1 0out

vin

vrefref

timet e


Implementing Logic LevelsImplementing Logic LevelsThe “0”s and “1”s in previous slides are merely symbols to represent two logical statessymbols to represent two logical states• e.g. the value 1/0, high/low, on/off, true/false,

hot/cold…hot/cold…

In actual circuit implementations, these “0”s and “1”s are represented by the voltageand 1 s are represented by the voltage (potential) presented at the output.• NOTE: There are other circuit implementations p

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 FamiliesLogic FamiliesThere are industrialindustrial standards on the voltage levels for grepresenting logic levels in di tdiscrete components.SSometimes referred as I/O standardsstandards.


Image source: http://www.interfacebus.com/voltage_LV_threshold.html

Own standard?Own standard?You can have your “own standard” when you build your own circuit e g :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 voltageUsually uses the maximum allowable voltage as “1”, and minimum allowable voltage as “0”Customary to label the max voltage as V orCustomary to label the max voltage as Vcc or Vdd

Minimum allowable voltage usually is 0 volt (notMinimum allowable voltage usually is 0 volt (not “0”).


Realistic Circuit I/O 1-bit ADCRealistic Circuit I/O 1 bit ADC10 0 1 0 1 0 1 0out

3 3

vin

3.3

vrefref

time

0

t e


Real CircuitsReal Circuits10 0 1 0 1 0 1 0out

3 3

vin

3.3

vrefref

time

0

t e


Quick Summary Quiz (1)Quick Summary Quiz (1)Which one is an example of discrete quantities?• Height of a personHeight of a person• Number of fingers

A• Area• Mass


Quick Summary Quiz (2)Quick Summary Quiz (2)Which of these statements is false?• Discrete values are easy to store,

transport.p• Enable very powerful and complicated

processing of inputprocessing of input.• Immune to a lot more interferences from

inside and outside of the system than aninside and outside of the system than an analog system.R l ti l f t th l t i• Relatively faster than analog systems in standard circuit implementations.


Quick Summary Quiz (3)Quick Summary Quiz (3)What does logic “1” represent?• 12 V• 3 5 V3.5 V• 1 V

All f th b• All of the above


Temperature Warning LightTemperature Warning Light

We want to turn on a warning light if the g gsurrounding temperature is too highWe’ll use a thermistor to senseWe ll use a thermistor to sense temperature around the systemThe resistance of a thermistor changes depending on its temperaturep g pIn this example, assume the resistance decreases as temperature increasesdecreases as temperature increases


System SpecificationsSystem SpecificationsThermistor (rt):• High temperature: High tempg p g p

rt = rmin = Rref / 3• Low temp

rt = rmax = Rref

Input stage:• Output “0” when temperature is high• Output “1” when temperature is low• Output 1 when temperature is low

Output stage:• Accept “1” to turn light on• Accept “0” to turn light off

Warning Light• Apply 9V to turn on• Apply 9V to turn on• Apply 0V to turn off


High Level DesignHigh Level DesignDigitally controlled thermo warning light

Process OutputInputTemp. Light

0, 1 1, 0

ADC DAC


High Level Design - InputHigh Level Design InputDigitally controlled thermo warning light


0, 1 1, 0

ADC DAC


Converting R to VConverting R to VVR

Temp. ADC outvin?

Thermistor changes its resistance according to t ttemperature

But…We want a change in voltage to be fed into our 1-bit ADC

One method: Use a potential divider to convert changes in R to changes in V


changes in R to changes in V

Review: Potential DividerReview: Potential Divideri

V1 V2 V3

Recall that current R1 R2 R3A B

1 2 3lR R R R= + +Qremains the same going through resistors in series

1 2 3

and total

AB total

R R R RV iR

V R

+ +

=

Q

11 1 1

1 2 3

ABAB

total

V RV iR R VR R R R

∴ = = =+ + The potential

22 2

1 2 3AB

RV iR VR R R

= =+ +

across each series resistor is proportional to it’s1 2 3

33 3 AB

RV iR VR R R

= =+ +

proportional to it s resistance


1 2 3R R R+ +

Converting R to V: Potential DivConverting R to V: Potential DivVcc

vout

Rref

v t =rt V

rt

vout Rref + rtVcc

Through a thermistor, the change in temperature (∆k) becomes a change in resistance (∆r )

0

becomes a change in resistance (∆rt)Then, through a potential divider, changes in resistance resistance (∆rt) is translated into change in vout.t out

Sanity check:• When rt is low (~0Ω), vout is low (~0V).• When r is high (>> R ) v is high close to V• When rt is high (>> Rref), vout is high, close to Vcc.


Complete Input StageComplete Input StageVcc Logical “0” “1”Rref

ADC outvout

rt

Once the resistance of the thermistor is 0

translated as voltage, it can feed our 1-bit ADC to convert into logical “1” and “0”Need to pick the right value for Rref to turn on/off ADC at right resistance


Quick Summary Quiz (4)Quick Summary Quiz (4)Which one can NOT be the threshold?

27

ccV

3ccV3

3 ccV8

3V34

ccV


Picking the ADC/resistor valuesPicking the ADC/resistor valuesVcc vout =Vcc

rmin

R + r=Vcc

Rref3

R + Rref=

Vcc

4Hi

Temp

Rref

ADCv

Rref + rmin Rref + ref3 4

vout =Vcc

rmax

R +=Vcc

Rref

R + R=

Vcc

2

p

LowTemp

rt

ADCvout Rref + rmax Rref + Rref 2Temp

A0 Set ADC threshold at 3Vcc

8Assume:

High tempr = r = R / 3 Hi “0”rt = rmin = Rref / 3

Low temp rt = rmax = Rref

Temp

LowTemp

0

“1”t max ref


e p

Quick Summary Quiz (5)Quick Summary Quiz (5)If we want the threshold at , which of 2

ccV

these statements is correct?• rmin = Rref / 3; rmax = Rref

2

min ref ; max ref

• rmin = Rref / 3; rmax = 2Rref R f

Vcc

min ref ; max ref

• r = R / 3; r = 3Rvout

Rref

• rmin = Rref / 3; rmax = 3Rref

R / 3 4R 0

rt

rt V• rmin = Rref / 3; rmax = 4Rref 0 vout =t

Rref + rtVcc


High Level Design - ProcessHigh Level Design ProcessDigitally controlled thermo warning light


0, 1, 2, 3 … 3, 2, 1, 0…

ADC DAC


Digital ProcessingDigital ProcessingRecall that the design of any subsystem is largely dependent on the system specifications:dependent on the system specifications:• (1) The intended function of the system• (2) The interface specification

In our example:• (1) System is to turn on a light bulb when temperature

is highis high• (2a) From input stage:

• high temp. “0”, low temp. “1”(2b) From output stage:• (2b) From output stage:

• “1” turns on light bulb, “0” turns off light bulb

Therefore, we need a digital processing stage thatTherefore, we need a digital processing stage that converts a “0” to “1”, and converts a “1” to “0”.


Converts “0” to “1”, vice versaConverts 0 to 1 , vice versaHow to make a processing stage that converts “zero” to the value “one”?zero to the value one ?Many ways:2 Calculate the output!2. Calculate the output!

out = −1× in +11. Use a logical NOT gate• (will come back to logic gates in a few weeks)• (will come back to logic gates in a few weeks)

in outin out


High Level Design - OutputHigh Level Design OutputDigitally controlled thermo warning light


0, 1, 2, 3 … 3, 2, 1, 0…

ADC DAC


Connecting to the OutputConnecting to the OutputSpecifications (given):• “1” 9V Light on1 9V Light on• “0” 0V Light off

Do not confuse between logical “1” with “1 volt”, g ,and logical “0” with “0 volt”.Logical values “0” and “1” should not be used to d i t t di tldrive output directlyThese internal discrete values (e.g. 18.9, 23, etc) must be translated into suitable analog outputmust be translated into suitable analog output values• Suitable V, I, R

A digital-analog convertor (DAC) converts discrete input values into analog output voltage values


Extremely Simple 1-bit DACExtremely Simple 1 bit DAC= 1?in Output 9V when input is “1”

Output 0V when input is “0”+-9V

voutp p

+

NOIN1in

+-9V

vcom

NCIN2

vout

Can effectively be implemented using a relay• A relay switch to NO (normal open) when the input

is activeOth i it it h t NC ( l l )• Otherwise it switch to NC (normal close)


Final System Block DiagramFinal System Block DiagramVcc

Rref

ADC invert DACv

rt

ADC invert DACvout

0

Straightly speaking a digital processing systemCan be made far more complex by moreCan be made far more complex by more elaborated ADC, DAC and digital processingCan be made far simpler by reducing the boundary b t b tbetween sub-systems.


Simple version – boundary breakingSimple version boundary breakingTemp. rt vADC procin procout vout

High low ~0 “0” “1” ~V (9 V)

Vcc

High low 0 0 1 Vcc (9 V)Lo high ~Vcc “1” “0” 0

Rref

rt

ADC invert DACvADC

0

rt

Can we bypass all intermediate stages?


Can we bypass all intermediate stages?

Simple Version – Single StageSimple Version Single StageVcc

Hi

rt

HiTemp rt → 0⇒ vout →Vcc

vout vout =Vcc

rlamp

rt + rlamp

rlampLow

t lamp

r →∞⇒ v → 0

Caveat:

Temp rt →∞⇒ vout → 0

Caveat:• resistance is not really 0 or infinite• Make sure enough current is available throughMake sure enough current is available through

lamp when rt is large1st semester, 2011 ENGG1015 - Dr. K. Wong 39

What if thermistor operates in opposite?What if thermistor operates in opposite?

Vcc

Rref

rt

ADC DACvADC

0

rt

Can we bypass all intermediate stages as before?


Can we bypass all intermediate stages as before?

Simple Version – Single Stage ??Simple Version Single Stage ??Hi

VccHi

Temp 0t outr v→∞⇒ →rt

vout =Vcc

rlamp

rt + rlamp

vout

Low

t lamp

0t tr v V→ ⇒ →rlamp

Temp0t out ccr v V→ ⇒ →

Not working !!


Complex versionComplex versionThe same digital processing structure is l li bl t l ialso applicable to complex processing

systemsFor example, we can alter the brightness of the warning lampbrightness of the warning lamp depending on the input temperature:• Higher temperature brighter lamp• Higher temperature brighter lamp

A multi-level ADC will be needed to obtain input temperature at higher precision


Complex Version (1)Complex Version (1)Input voltageR l t d t t t

0,1,2,3…Related to temperature 0,3,5,6…

RrefRref

rt

ADC invert DACvADC

rt

ADC Process DACvADC

0

rt

0

rt


Complex Version (2)Complex Version (2)vout is not

7Output Voltage vs Temperature

linearly proportional to 5

67

p ptemperature

234

Need digital processing to 0

1

p glinearize it before outputbefore output to the lampvout =

rtRref + rt

Vcc


f

Output Stage ImplementationOutput Stage ImplementationIn general DACsare quite = 3?are quite complicatedOne of many

= 3?

+-12V

One of many designs: = 2?

+8V -8V

= 1?

+-4V

= 0?= 0?

+-0Vin vout


In conclusion…In conclusion…All electronic/electrical systems can be di id d i t th i b t i tdivided into three main sub-systems: input, process, outputAnalog systems manipulate analog signals throughoutDigital systems handles digital data in process stageprocess stage1-bit ADC can be implemented using i l tsimple comparator

Logical values ≠ electrical valuesg


Administrative AnnouncementsAdministrative Announcements

http://www.eee.hku.hk/~engg1015p gg


Administrative AnnouncementsAdministrative AnnouncementsLabs

Be on time!Yes, it was a bit tough as a first lab, g• Next week will be (hopefully) shorter…• You need the skills for your projecty p j

Not absolutely required to attend the lab with your group project partnersy g p p j p• You might make new friends there too!

No make-up lab!No make up lab!• If you miss your lab session without good

reason, we will not grade your lab afterwardg y


Administrative AnnouncementsAdministrative AnnouncementsProject

Project will start in week 7 (Oct 10)Project will start in week 7 (Oct 10)You must have a project group by thenGroup size is four (4, quattro, 四) peopleGroup size is four (4, quattro, 四) peopleYou get penalized for any more or less than 4• If you have 3 or 5 people, you get 20% discount on your

project gradeproject grade• If you have 2 people, you get 50% discount on your project

gradeThe only reason there will be a group size not equal to 4 is when the class size is not multiple of 4.• Only one (1) team will be chosen in week 7 to allow a group

i f ≠ 4size of ≠ 4We reserve the right to change the rule at will


electronic systems example:electronic systems …engg1015/fa11/handouts/03-exelecsys.pdfelectronic...

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