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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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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*
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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*
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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%
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" # $ 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 (%)!.
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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*
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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*
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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.
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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.
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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.
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• 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$2* J - K (
T & conductor temperature ' K ( /dd 20* to
B & Bandwidth of sstem ' Hz (
Pn =k
T B
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• #rom the stu$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 .
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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
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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.
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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.
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+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)*
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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+ &
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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=
=
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&oise Cac!ation 5n A"pifier
o To types of "ode
$ &oise a"pifier 6ode*
$ &oiseess a"pifier "ode*
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nalysis of Noise m!lifier /o$el
)()(
and
0
0
aii
a
iai
i
N N GG N N G N GN N
GS S
+=+=+=
=
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nalysis of Noiseless m!lifier /o$el
)(and
0
0
aii
i
N N G N
GS S
+=
=
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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( −=
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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 *
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)(
)(
)(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
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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
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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 *
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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
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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
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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
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Contd***
4e aso can cac!ate by !sin# thisfooin# e/!ation>
α =dB
L
%here
ℓ & transmission medium len6th α & attenuated constant
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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.
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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.
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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.
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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
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