chapter 1 part 2.1-noise v2

8/16/2019 Chapter 1 Part 2.1-Noise v2

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CHAPTER 1 (cont…)CHAPTER 1 (cont…)Part 2.1Part 2.1 NoiseNoise


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Objectives

• To differentiate the types of noise

• To cac!ate the ther"a noise

#enerated by a resistor• To cac!ate the si#na$to$noise ratio

(%&R) and noise fi#!re for an

a"pifier


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'ect!re overvie

• Types of noise

• Ther"a noise• %i#na$to$noise ration (%&R) and

noise fi#!re


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Introduction

Noise can be defined as

• undesired random variations that interface with the

desired signal and inhibit communication.

Where does noise originate in a communication

system?

• Channel @ transmission medium

• Devices @ Equiments


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Contd***

Noise Effect• !ne of the main limiting factor in

obtaining high erformance of a

communication system.• Decrease the quality of the receiving

signal.


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7/48

Contd***

• &oise+ interference and distortion, Noise

• Refers to rando" and !npredictabeeectrica si#nas prod!ced by nat!raprocess*

• %!peri"posed on infor"ation bearin#si#na+ the "essa#e partiay corr!pted ortotay erased*

• Can be red!ced by fiterin# b!t canttotay ei"inated*


8/48

Contd***

, Interference

• A conta"ination by e-traneo!s si#nas

fro" h!"an so!rces (e*#* fro" otherT-+ poer ines+ "achineries)

• Often occ!rred in radio syste" hoseR- antenna intercept severa si#nas

at the sa"e ti"e*


9/48

Contd***

, Distortion

• The si#na pert!rbation ca!sed byi"perfect response of the syste" to the

desired si#na*• .isappear hen the si#na is t!rned$off*

• Can be corrected by the e/!ai0ers*


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&oise Re"edies

RE.2CE 3A&.45.TH

5&CREA%E TRA&%65TTER% PO4ER

'O4 &O5%E A6P'575ER%


11/48

" # $ C % E & N ! $ ' E

( t u b e s

' ) ! * N ! $ ' E

( e l e c t r o n i c s y s t e m( e q u i m e n t

* ) E & + , # N ! $ ' E

( t r a n s i s t o r ( d i o d e

( r e s i s t o r s

$ N * E & N , #

, * + ! ' - ) E & $ C N ! $ ' E

( N o i s e b l a n . i n g

( l i g h t i n g

' - , C E N ! $ ' E

( s o l a r n o i s e( s . y n o i s e

+ , N + , D E N ! $ ' E

( a u t o m o b i l e e n g i n e( e l e c t r i c m o t o r

( c o m u t e r

E / * E & N , #

N ! $ ' E

y!es of N"ISE


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Contd***

, &oise #enerated o!tside the eectronice/!ip"ent !sed*

, %o!rce can be terrestria ore-traterrestria (E*#* the earth+ the "oon+the s!n+ the #aa-ies)*

, .o not effect the entire co""!nication

fre/!ency spectr!" b!t affect certainfre/!encies at certain ti"es and ocations*, Types8 6an "ade noise+ space noise+

at"ospheric noise*


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Contd***

a* 6an "ade noiseo Produced by mankind

o Source : Spark-producing mechanisms

oImpulsive in nature & contains a widerange of frequencies propagatedthrough space.

o Sometimes called industrial noise

metropolitan & industrial area!.


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Contd***

b* %pace noiseo "he sun is a powerful source of

radiation.

oStars also radiate noise calledcosmic# stellar or sky noise.

o Important at higher frequencies$% and above! because

atmospheric noise dominates atlower frequencies.


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Contd***

c* At"ospheric noiseo "he principle source is lightning

a static electricity discharge.

o'an propagate for a long distancesthrough space.

o"he lightning energy relatively lowfrequency up to several (%)!.


16/48

Contd***

$ Eectronic noise #enerated by thepassive and active co"ponentsincorporated in the desi#ns of

co""!nications e/!ip"ent*$ Types 8 %hot noise+ fic9er noise+

ther"a noise*


17/48

Contd***

• %hot &oiseo Ca!sed by a rando" arriva of carriers

(hoes and eectrons) at the o!tp!t of aneectronic devices*

o Rando"y varyin# : s!peri"posed ontoany si#na present*

o %o"eti"es caed transistor noise*


18/48

Contd***

• 7ic9er noise

o *+cess noise that related to dc

current ,ow through imperfectconductors.

o "he real nature of ,icker noise not yet fully understood.


19/48

Thermal Noise

• "his type of noise arise due to therandom motion of free electrons in theconducting medium such as resistor.

• *ach free electron inside a resistor isin motion due to its thermal energy.

• "he path of electron motion is randomand )ig-)ag due to collision with thelattice structure.


20/48

Contd***

• "he net eect of the motion of allelectrons constitutes an electriccurrent ,owing through the resistor .

• It causes the rate of arrival of electronat either end of a resistor to varyrandomly and thereby varies theresistors potential dierence. "hat is

the direction of current ,ow is randomand has a )ero mean value.


21/48


22/48

• Thermal noise also known as Johnson noise or white noise.

• In 1928, J.B. Johnson founded that Noise Power is directproportionall with temperature and !andwidth.

• Noise spectrum densit is constant for all "alue of

fre#uenc to 1$12 Hz .

•

%here

P n & noise power 'Watt (

k & Bolt)man constant '1.*8 + 1$2* J - K (

T & conductor temperature ' K ( /dd 20* to

B & Bandwidth of sstem ' Hz (

Pn =k

T B


23/48

• #rom the stu$y of circuit theory% therelationshi! &et'een source resistor an$matche$ loa$ un$er maximum !o'er transfer

is 'hen(

n )(

* .

• he total of noise source !o'er is P n .


24/48

kTBRV

kTBRV

kTB R

V

kTB P P

R

V

R

V

R

V P

V

V R R

R

V

n

n

n

Ln

n

n

L

L

n

n

Ln

L

L

4

4

4

therefore

and4

2,VatPower

2

2

2

2

2

2

L

=

=

=

==

=

==

=+=

3nown as 4n & 45 & 4,

Therefore "olta6e at 45 is


25/48

E-a"pe 1

• A receiver has a BW of 10 kHz

with the 4.14 x 10-17 W noise

power. A resistor that matches thereceiver input impedance is

connected across its antenna

terminals. Calculate the resistor’s

temperature in Celsius.


26/48

E-a"pe ;

• A 1 kΩ resistor is connected across

1 kΩ antenna input of a television

receiver. The BW of the receiver is 5MHz and the resistor at the room

temperature 293 K. Calculate the

noise power and noise voltage

applied to the receiver input.


27/48

+o' to ,uantifying the Noise-

• The presence of noise de#rades theperfor"ance of anao# and di#itaco""!nication*

• The e-tent to hich noise affects theperfor"ance of co""!nication syste"s is"eas!red by the o!tp!t si#na to noise poerratio or %&R (for anao# co""!nication

syste"s) and probabiity of error (for di#itaco""!nication syste"s)*


28/48

Contd***

• The si#na /!aity at the inp!t of the receiver ischaracteri0ed by the inp!t si#na to noise ratio*3eca!se of the noise so!rces ithin the receiver+hich is introd!ced d!rin# the fiterin# anda"pification processes+ the %&R at the o!tp!t of

the receiver i be oer than at the inp!t of thereceiver*

• This de#radation in the si#na /!aity ischaracteri0ed in ter"s of noise e/!ivaentbandidth+ &


29/48

Noise Calculation

• %&R is ratio of si#na poer+ % to noise poer+ & *

• &oise 7actor+ 7

• &oise 7i#!re+ &7

dB N

S SNR log10=

oo

ii

N S

N S F =

)(log10

log10

dB N S

N S

F NF

oo

ii=

=


30/48

&oise Cac!ation 5n A"pifier

o To types of "ode

$ &oise a"pifier 6ode*

$ &oiseess a"pifier "ode*


31/48

nalysis of Noise m!lifier /o$el

)()(

and

0

0

aii

a

iai

i

N N GG N N G N GN N

GS S

+=+=+=

=


32/48

nalysis of Noiseless m!lifier /o$el

)(and

0

0

aii

i

N N G N

GS S

+=

=


33/48

i

ai

i

aii

aii

i

i

i

i

N

N

N

N N

N N G

GS

N

S

SNR

SNR F +=+=

+

== 1

)(0

7N4$ 7N4i

/s known as BkT N BkT N eaiii

== and

i

e

i

e

i

ai

T

T

BkT

BkT

N

N F

+=+=+= 111Noise actor,

Noise Temperature, ie T F T )1( −=


34/48

nalysis of Casca$e Stages

• Consi$er three t'o !orts in casca$e

G3

S o

N o

G1 F 2 , G2 , T e2

antenna

re(amlifier demodulator amlifier

F 1, T

e1 F

3, T

e3

S i

N i

T i

N ai1

N ai2

N ai3

S 1

N 1

S 2

N 2

7ta6e 1 7ta6e 2 7ta6e *


35/48

)(

)(

)(Power, Noise

Power,Signal

11

11

111

11

ei

ei

aii

i

T T kBG

BkT BkT G

N N G N

S GS

+=+=

+==

7ta6e 1


36/48

BkT GT T kBGG

N G N G

N N G N

S GGS GS

eei

ai

ai

i

22112

2212

2122

12122

)(

)(Power, Noise

Power,Signal

++=+=

+===

7ta6e 2


37/48

BkT G BkT GGT T kBGGG

N G N G

N N G N

S GGGS GS

eeei

ai

ai

i

332231123

3323

3230

123230

)(

)(Power, Noise

Power,Signal

+++=

+=

+=

==

7ta6e *


38/48

Noise #actor% #

i

e

i

e

i

ei

i

eeei

kBT GkBT GGT T kBGGGS GGG

BkT S

N S

N

S

O

itotal

T GG

T

T G

T

T

T T

kBT GGG

kBT GkBT GGT T kBGGG

SNRSNR F

eeei

i

i

i

O

O

i

i

12

3

1

21

123

332231123

)(

)(

332231123

123

+++

=

+++=

=

==

+++


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21

3

1

2

1

0

0

21

3

1

21

21

3

1

21

)1()1(

)1( therefore

290 and 1If

1

G G

F

G

F F F

T F T

K T T T

T

F

T G G

T

T G

T

T

T F

T G G

T

T G

T

T

T

T

T F

TOTAL

e

i

i

e

i

e

i

e

i

e

TOTAL

i

e

i

e

i

e

i

i

TOTAL

−+

−+=∴

−=

°==+=

+++=

+++=

3nown as the o"erall noise factor, T:T/5


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21

3

1

21

021

3

01

2

0

1

0

21

0

3

1

0

2

0

1

0

21

3

1

2

1

1111

11

)1()1(

GG

T

G

T T T

T GG

T

T G

T

T

T

T

T

GG

T

T

G

T

T

T

T

T

T

GG

F

G

F F F

ee

eeTOTAL

eeeeTOTAL

ee

eeTOTAL

TOTAL

++=

++=

−+

+

−+

++=+

−+

−+=

/nd we can calculate noise temperature, T e


41/48

12121

3

1

21

...

)1(...

)1()1(

−

−++

−+

−+=

n

n

GGG

F

GG

F

G

F F F

It can also !e shown that the o"erall noise fi6ure, F

and the effecti"e noise temperature, T e of n networks

in cascade is 6i"en !;

12121

3

1

21

......

−

++++=n

enee

eeGGG

T

GG

T

G

T T T


42/48

ransmission *oss% ttenuator

• Every trans"ission "edi!" i prod!ce poeross*

P o!t = P in *

Poer oss or atten!ated is #iven by thefooin# e/!ation8

G P

P L

out

in 1==

dB

out

in

dB G P

P L −=

= 10log10


43/48

Contd***

4e aso can cac!ate by !sin# thisfooin# e/!ation>

α =dB

L

%here

ℓ & transmission medium len6th α & attenuated constant


44/48

E-a"pe ?

Determine:

a. Noise Figure for an equivalent

temperature of 75 K (use 290 K for the reference temperature).

b. Equivalent noise temperature

for a Noise Figure of 6 dB.


45/48

E-a"pe @

For three cascaded amplifier stages,

each with noise figure of 3dB and

power gain of 10 dB, determine the

total noise figure.


46/48

E-a"pe

An amplifier consists of three identical

stages in tandem. Each stage having

equal input and output impedances. For

each stages, the power gain is 8 dB whencorrectly matched and the noise figure is

6dB. Calculate the overall power gain and

noise figure of the amplifier.


47/48

t the en$ of this

cha!ter% you shou$ &ea&le• To differentiate the types of noise

• To cac!ate the ther"a noise#enerated by a resistor

• To cac!ate the si#na$to$noise ratio

(%&R) and noise fi#!re for ana"pifier


48/48

chapter 1 part 2.1-noise v2

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