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Communication Circuits
Ahmed Muhammed Almanasreh
EE Dept.
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Ch1: Introduction
Importance o' comm.(istor)
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Elements of comm. system
In
Mod
Carrier
Amp
Channel
Amp AmpDeMod Out
Tx
Rx
Analog:
AM,M
!igital:
"M,"CM
re#uency
Mode
of Tx
Mux
$ire %s
$ireless
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Introduction
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Channel
*ine +!ire, Radio +!ireless,
Adanta-es:
*o! path loss
*o! inter'erence
ath charac. Are stale
0 reuse is simple
Adanta-es:
Cheap and uic3 to implement
a)leaes and plannin- issimple
Inherent 0C potentialMoile
et!or3s easil) recon-ured
Disadanta-es:
*a)in- lines is e6pensiea)leaes and plannin- iscpl6
Comple6 0C
o moilit)
Di7cult net!or3
Disadanta-es:
ath loss is lar-eInter'erence is a seriousprolem
0 reuse is not eas)
ath charac. Are ariale
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1&' Ty(es of Elect. Comm.
" cate-ori8ations: 9ne!a) or 2!a)
Analo-di-ital
0aseandmodulated
Simple6duple6
Analo-: denition;e6amples
Di-ital: e6amples
0aseand: e6amplesModulation:
ractical reali8ation
Channel utili8ation
0etter per'ormance
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A((lications ) EM *(ectrum
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+and !esignations
0and!idth: si-nal;euipment; channel
More applications;more deelopment;more channels; hi-h'reuencies
0 is proportional to'
Spectrumassi-nment
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Ch: AM ) **+
Modulation: denition AM !ith sine !aes
Math representation
AM !ith di-ital si-nals:AS
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& Modulation index
Inde6; m>?m/?c Inde6 measurement
ercenta-e o' modulation
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&' *ide-ands
*o!er and upper sideands #reuenc) and timedomains
0
(armonics
o!er distriution %> C@ *S0@ S0 S0> *S0> C+m2,/4
AM e7cienc)
%> C+1@ m2/2,
1BB mod is di7cult in
practice o constant amplitudes
Applications: AM radioroadcastin-; C0 radio; %?0C; aircra't comm;modems
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&/ **+ Communications
%o increase e7cienc);suppress carrier: DS0SC
More e7cienc); eliminateredundanc): SS0SC
%ime and 'reuenc) si-nals
DS0 is eas) to -enerateut di7cult to recoer
SS0 enets:
Saes spectrum
(i-her eF G -reaterdistance
*ess noise
*ess 'adin-
o R# si-nal is transmittedi' no si-nal is present
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**+%ime and 'reuenc) domain
si-nals
SS0 po!er:
no carrier
sinusoidal modulation
oice modulation: pea3
enelope po!er +E, atoice amplitude pea3s
E > ?rms2/R
In terms o' modulator circuit
Aera-e po!er; Ia->E/+" or 4,
Applications:SS0: telephone; 2!a) radio+militar); C0 radio; amateurs,
DS0: #M and %? stereo
?S0
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Ch': AM Circuits'.1: Modulators
%!o asic !a)s to produceAM Analo- Multiplication
onlinear Mi6in-
Analo- Multiplication Consider the AM cure; #i- 2.1 Math representation
AM: passin- a carrier throu-h act !ith -ain proportional to
modulatin- si-nal *o! leel: DiFerential amplier;
olta-e diider I
(i-h leel E6: Collector mod.
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Ch': AM Circuits'.1: Modulators: !AM
DiFerential Ampliers #i-. ".4a
9peration
Math rep.
0alanced or diFerentialoutput
Sin-leended op
2 ops are 1Boout o'phase
Hain is 'unction o' IE
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Ch': AM Circuits'.1: Modulators: !AM
DiFerential AmplierModulator #i-. ".4
9peration
Modulatin- si-nal aries
-ain Modulatin- si-nal amplitude
determines carrieramplitude
Results in AM
%uned ct is reuired atoutput
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Ch': AM Circuits'.1: Modulators: "I0 diode
I Diode Diodes 'or (#
?ariale resistance
Concept as a mod.
I Diode Mod. #i-ure "$a 9peration
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Ch': AM Circuits'.1: Modulators: "I0 diode
I Diode Mod. #i-. ".$
Enhanced con-uration
Maintains constant ctimpedance
Characteristics (i-h 'reuenc): ?(#; (#
(i-h attenuation
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Ch': AM Circuits'.1: Modulators: igh le%el
Amplication is reuired
earl) e'oretransmission
#i-. "&
*inear amplication
should e used not todistort the si-nal
Amp. Class: A; A0. 9r 0
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Ch': AM Circuits'.1: Modulators: Collector igh le%el
Modulation ta3es placeat nal R# sta-e o' %6.
#i-. "
Class C amp is used
9peration1BB modulation
reuires olta-e appliedto collector > 26?cc +#i-
".,
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Ch': AM Circuits'.1: Modulators: Collector igh le%el
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Ch': AM Circuits'.1: Modulators: 0onlinear mixing
#E%: Suare la! response
#i-. "1Diode Mod.
#i- ".2
9peration
ae'orm rep.
%uned ct*imitations usin- math
anal)sis p to Suare term onl)
cJ"m
o 1BB modulation