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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