Intro to Electronic Comm_part2
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Transcript of Intro to Electronic Comm_part2
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8/20/2019 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
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