Intro to Electronic Comm_part2

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    1.7 Noise – Representation, types & source

    ◦Definition – any undesirable electrical energy that falls within the passband of the signal.

    ◦Effect of noise on the electrical signal :

    ◦2 general categories of noise :

    ◦ Correlated noise – noise that exists only when a signal is present.

    ◦ Uncorrelated noise – noise that presents all the tie whether there is a signal or not

    !hapter 1 : "ntro#uction to

    !ounications $yste%E! '('' !ounication $yste

    )aculty of Electrical Engineering 1

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    1.7.1 *ncorrelate# noise

    ◦2 general categories of uncorrelate# noise :

    ◦ 1. External noise – noise that generate# outsi#e the #e+ice or circuit.

    Atmospheric noise

    - naturally occurring electrical #isturances that originate within earth-s atosphere such as lightning.

    - also nown as static electricity.

    Extraterrestrial noise

    -

    consists of electrical signal that originate fro outsi#e earth-s atosphere an# therefore also nown as #eep/space noise.

    - 2 categories of extraterrestrial noise.

    i – solar noise – noise that generate# #irectly fro the sun-s heat.

    ii – cosmic noise / black-body noise – noise that is #istriute# throughout the galaxies.

    Man-made noise

    / noise that is pro#uce# y anin#.

    / source : spar/pro#ucing echanis 0coutators in electrical otors, autooile ignition

    systes, ac power generatingswitching euipent, fluorescent lights3.

     

    2

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    1.7.1 *ncorrelate# noise

    ◦2 general categories of uncorrelate# noise :

    ◦ 2. Internal noise – noise that generate# within the #e+ice or circuit.

    Shot noise

    - cause# y the ran#o arri+al of carriers 0holes an# electrons3 at the output eleentof anelectronic #e+ice.

    - shot noise is ran#oly +arying an# is superipose# onto any signal present.

    ransit-time noise

    - irregular, ran#o +ariation #ue to any o#ification to a strea of carriers as they passfro theinput to the output of a #e+ice.

    - this noise ecoe noticeale when the tie #elay taes for a carrier to propagate through a#e+ice is excessi+e.

     

    '

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    1.7.1 *ncorrelate# noise

    ◦2 general categories of uncorrelate# noise :

    ◦ 2. Internal noise – noise that generate# within the #e+ice or circuit.

    hermal / random noise

    - associate# with the rapi# an# ran#o o+eent of electrons within a con#uctor #ue to theralagitation.

    - also nown as %rownian noise, 4ohnson noise an# white noise.

    - uniforly #istriute# across the entire electroagnetic spectru.

    - a for of a##iti+e noise, eaning that it cannot e eliinate#, an# it increase in intensity withthe nuer of #e+ices an# with circuit length.

    - the ost significant of all noise sources

    - theral noise power can e #efine# as follow :

    0(.13

    where N : noise power 0watts3

      % : an#wi#th 05ert63

      : asolute teperature 0el+in3 .......... 8 9! 27'9

    ;

     KTB N   =

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    1.7.1 *ncorrelate# noise

    hermal / random noise

    - eui+alent circuit for a theral noise source when the internal resistance of the source R 1 is in

    series with the rs noise +oltage

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    1.7.2 !orrelate# noise

    ◦a for of internal noise that is correlate# to the signal an# cannot e present in a

    circuit unless there is a signal.◦ pro#uce# y a nonlinear aplification resulting in nonlinear #istortion.

    ◦ there are 2 types of nonlinear #istortion that create unwante# freuencies that

    interfere with the signal an# #egra#e the perforance :

    ◦1. !armonic distortion

    ◦ occurs when unwante# haronics of a signal are pro#uce# through nonlinear

    aplification.

    ◦ haronics are integer ultiples of the original signal. he original signal is the first

    harmonic 0fun#aental haronic3, a freuency two ties the fun#aental freuency

    is the second harmonic, three ties is the third harmonic an# so on.

    ◦ Distortion easureents :

    $yste (

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    1.7.2 !orrelate# noise

    ◦1. !armonic distortion

    #istortion easureents :/ Nth haronic #istortion 8 ratio of the rs aplitu#e of Nth haronic to the rs aplitu#e of

    the fun#aental.

    / otal 5aronic Distortion 05D3

    0(.;3

    where

    all in rs +alue.

    $yste 7

    1>>?   ×=l   fundamenta

    higher 

    v

    vTHD

    2;;

    ''

    22   ....   nhigher    vvvvv   ++++=

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    1.7.2 !orrelate# noise

    ◦2. Intermod"lation distortion

    intero#ulation #istortion is the generation of unwante# su an# #ifferencefreuencies pro#uce# when two or ore signals ix in a nonlinear #e+ice 0cross

     pro#ucts3.

    ◦ unwante# @

    $yste A

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    1.7.' Bther type of noise

    ◦1. Imp"lse noise

    characteri6e# y high aplitu#e peas of short #uration 0su##en urst of irregularlyshape# pulses3 in the total noise spectru.

    ◦ coon source of ipulse noise : transient pro#uce# fro electroechanical switches

    0relays an# solenoi#s3, electric otors, appliances, electric lights, power lines, poor/

    uality sol#er Coints an# lightning.

    ◦2. Inter#erence

    ◦ electrical interference occurs when inforation signals fro one source pro#uces

    freuencies that fall outsi#e their allocate# an#wi#th an# interfere with inforation

    signal fro another source.

    ◦ ost occurs in the ra#io freuency spectru.

    $yste

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    1.A Noise araeters

    1.A.1 $ignal/to/noise ower Ratio

    ◦ signal/to/noise power ratio 0$N3 is the ratio of the signal power level to the noise power level  

    and can be epressed as

    0(.=3

    in logarithic function

    0(.(3

    in ters of +oltages an# resistance

    0(.73

    in the case R in 8 R out, 0(.73 can e re#uce# to

    0(.A3

    $yste 1>

    n

     s

     ! 

     ! 

     N 

    " =

    n

     s

     ! 

     ! dB

     N 

    " log1>30   =

       

      

     =

    out n

    in s

     RV 

     RV dB

     N 

    log1>30

    2

    2

       

      =

    n

     s

    V dB

     N 

    " log2>30

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    1.A.2 Noise )actor an# Noise )igure

    ◦ Noise factor  is the ratio of input signal#to#noise ratio to output signal#to#noise ratio

    0(.3

    ◦  Noise figure is the noise factor stated in dB and is a parameter to indicate the

    $uality of a receiver 

    0(.1>3

    ◦ Noise )igure in "#eal an# Non/i#eal Fplifiers

    / an electronic circuit aplifies signal an# noise within its passan# eually well

    / in the case of i#ealnoiseless aplifier, the input signal an# the noise are

    aplifie# eually.

    / eaning that, signal/to/noise ratio at input 8 signal/to/noise ratio at output

    $yste 11

    out 

    in

     N "  N "  % 3030=

        

      ==

    out 

    in

     N " 

     N "  %  N% 30

    30log1>log1>

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    1.A.2 Noise )actor an# Noise )igure

    ◦ Noise )igure in "#eal an# Non/i#eal Fplifiers 0continue3

    / in reality, aplifiers are not i#eal, a##s internally generate# noise to the

     wa+efor, re#ucing the o+erall signal/to/noise ratio.

    / in figure 0a3, the input an# output $N ratios are eual.

    $yste 12

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    1.A.2 Noise )actor an# Noise )igure

    ◦ Noise )igure in "#eal an# Non/i#eal Fplifiers 0continue3

    / in figure 03, the circuits a## internally generate# noise N#

     to the wa+efor,

    causing the output signal/to/noise ratio to e less than the input signal/to/noise

      ratio.

    !hapter = : Digital !ounication

    $yste 1'

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    1.A.2 Noise )actor 0)3 an# Noise )igure 0N)3

    ◦ Noise )igure in !asca#e# Fplifier 

    / when two or ore aplifiers are casca#e# as shown in the following figure,

    the total noise factor is the accuulation of the in#i+i#ual noise factors.

    / )riss- forula is use# to calculate the total noise factor of se+eral casca#e

    aplifiers

    0(.113

    $yste 1;

     N 

     N T 

     & & &

     % 

     & &

     % 

     &

     %  %  % 

    ...

    1...

    11

    2121

    '

    1

    21

    −++

    −+

    −+=

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    1.A.2 Noise )actor an# Noise )igure

    ◦ Noise )igure in !asca#e# Fplifier 0continue3

    / the otal Noise )igure

    0(.123

    Ghen using )riss- forula, the noise figures ust

     e con+erte# to noise factors @@@

    $yste 1=

    T T    %  N%    log1>=

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    1. Exaples

    ◦Ex 1 : !on+ert the following teperatures to el+in : 1>>9 !, >9 ! an# /1>9 !.

    $yste 1(

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    1. Exaples

    ◦Ex 2 : )or an# electronic #e+ice operating at a teperature of 179 !, with a

     an#wi#th of 1> 56, #eterine

    a. theral noise power in watts an# #%.

     . rs noise +oltage for a 1>> H loa# resisstance.

    $yste 17

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    1. Exaples

    ◦Ex ' : )or an aplifier with an output signal power of 1> G an# output noise

     power of >.>1 G, #eterine the signal/to/noise power ratio.

    $yste 1A

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    1. Exaples

    ◦Ex ; : )or an aplifier with an output signal +oltage of ;.>>= < an# an input an# output resistance of => , #eterine the signal/to/

    noise power ratio.

    $yste 1

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    1. Exaples

    ◦Ex = : )or a non/i#eal aplifier with a following paraeters, #eterine

    a. input $N ratio 0#%3 . output $N ratio 0#%3

    c. noise factor an# noise figure

    "nput signal power 8 2 x 1>/1> G

    "nput noise power 8 2 x 1>/1A G

    ower gain 8 1>>>>>>

    "nternal noise N# 8 ( x 1>/12 G

    $yste 2>

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    1. Exaples

    ◦Ex ( : )or ' casca#e# aplifier stages, each with a noise figures of ' #% an#

     power gain of 1>#%, #eterine the total noise factor an# noise figure.

    $yste 21