슬라이드 제목 없음 - cho, jun dong ??? sungkyunkwan...

CNU Dept. of Electronics

D. J. Kim1

Lecture on Communication Theory

Chapter 3. Continuous-wave modulation

3.1 Introduction

modulation: the process by which some characteristic of a carrier is varied in accordance with a

modulating wave(signal)

3.2 Amplitude Modulation

1. Am1) Sinusoidal carrier wave c(t)=Ac cos(2fct)

2) AM signal s(t) =Ac [1+ka m(t)] cos(2fct)

m(t)baseband

m(t)cos(wct)passband

cos(wct)

carrier frequencycarrier amplitude

message signalamplitude sensitivity


D. J. Kim2


3) s(t) 의 envelop 이 m(t) 와 똑같은 shape 이 될 조건a) | Kam(t) | < 1 for all t

b) fc >> W where W is message BW


D. J. Kim3


4) 주파수상에서의 표현

ex1) Single-Tone Modulator message m(t)=Am cos(2f m t )

AM s(t)=Ac [1+cos(2f m t)]cos(2fc t) Where = kaAm ; Modulation factor

100 = 100 kaAm ; percentage Modulation

)] (M ) ([M2Ak )] ( ) ( [

2A S(f) cac

cccc ffffffff

BT=2W


D. J. Kim4


modulation 100%1 if

power totalpower band side total

31

2 2

2

A 81 power frequency -side-Lower

A 81 power frequency -side-Upper

A21 power Carrier

2c

2

2c

2

2c


D. J. Kim5


2. Switching Modulation

v1(t) = Accos(2(t)) + m(t))

If m(t) Ac

v2(t) v1(t), c(t) > 0

0, c(t) <0

v2(t) [AC cos(2(t)) + m(t))] gTo(t)

where T0=1/fc

m(t)

BPF[v2(t)]


D. J. Kim6


Diode function

By Fourier series

1n2tf2cos1n2

121

c1n

1n

2 (t)gTo

signal AM

(t)vBPF

)cos(6 )cos(4

2

cff2 )tf2cos()t(mA41

2A

)tf()tf(

)t(m21)tf2cos()t(m

A41

2A

1n2tf2cos1n2

121)t(mtf2cosA)t(v

cc

c

cc

cc

c

c1n

1n

cc2

on off


D. J. Kim7


3. Envelope Detector : AM radio receiver

Charging time constant = (f + RS ) C

For Rapid charge (f + RS )C << 1/fc

Discharging time constant =

BW message Wwhere

W1CR

f1

l

c

CRl


D. J. Kim8



D. J. Kim9


3.3 Virtues, Limitations , and Modifications of AM

1. Virtues 1) easy modulator: switching mod, square-law modulator demodulator: envelop detector, square-law detector2) relatively cheap

2. Limitations1) Wasteful of power carrier power2) Wasteful of BW 1/2 로 줄일 수 있다 .

LSB 와 USB 가 symmetry.

3. Modifications of AM1) DSB-SC modulation : no carrier2) VSB modulation : BW 를 약 1/2 로3) SSB modulation : BW 를 1/2 로


D. J. Kim10


3.4 DSB - SC Modulation

1. DSB - SC signal

)t(m)tf2cos(A)t(m)t(c)t(s

cc

)ff(M)ff(MA21)f(S ccc


D. J. Kim11


2. Ring Modulator

c(t) > 0 s(t)=m(t)

c(t) < 0 s(t)= -m(t)

+ -


D. J. Kim12


c(t) =

BPF[s(t)] =BPF[c(t)m(t)] f=fc

= m(t)

( 주의점 ) Transformers are perfectly balanced and diodes are identical no leakage of modulation frequency into modulator output

]1n2tf2cos[1n2

)1(4c

1n

1n

tf2cos4c

2W2W

-fc fc 3fc-3fc

w

-3fc

M(f)

S(f)


D. J. Kim13


3. Coherent detection or synchronous demodulation

frequency coherent detection

'ff cc

null quadrature

;0)t(v90if

)t(m2

1'AA21)t(v45if

)t(m'AA21)t(v0if

)t(m]cos['AA21)t(v

00

cc00

cc0

cc0

LPF

)t'f2cos('A)t(c cc Local Osc

)(0 tv)t(s

)t(m]t)'ff(2cos['AA21)]t(v[LPF)t(v cccc0

)t(m)tf2cos(A)t'f2cos('A)t(v cccc

)t(mt)'ff(2cos'AA21

cccc

)t(mt)'ff(2cos'AA21

cccc =

+

)t(v


D. J. Kim14


Coherent Detection 특징 : perfect demodulation but 복잡 cost

4. Costas Receiver

)t(m'AA21)t(v

0,'ff

cc0

cc

: coherent phase &frequency

00Q

)t(mI: torDiscrimina Phase

real : m(t)근거구현

V(f)

2wf-2fc 2fc

2w


D. J. Kim15


sin

1sin

)t(mcos)t(msin

, φφsin1φcos

,

channel Ichannel Q small for

빠른 주파수

늦은 주파수 정상주파수

s(t)

OSC

450

- 450


D. J. Kim16


5. Quadrature-Carrier Multiplexing or QAM

)tf2sin()t(mA)tf2cos()t(mA)t(s c2cc1c

In-phase Quadrature


D. J. Kim17


Key points> Correct phase & frequencyCostas Receiver 사용

Send a pilot signal outside the passband of the modulated signalPilot : Low power sinusoidal tone whose frequency and phase are

related to c(t)Add pilot signal of small carrier

3.5 Filtering of side-bands

)t(m21)t(r

)t(m21)t(r

)tf4sin()t(m21)tf4cos()t(m)t(m

21

)tf2cos()tf2sin()t(m)tf2cos()tf2cos()t(m)tf2cos()t(s)t(r

22

11

c2c1

cc2cc1

c

LPF

LPF

<Band pass filtering>


D. J. Kim18


1.BPF 의 LSB 와 USB 가 symmetric 할 경우

2. BPF 의 LSB 와 USB 가 unsymmetric 할 경우

H(f)

-fc fc

f

LPFm(t) s(t)

)tf2cos(A cc

0

-fc fc

FILTERHQ(T)

FILTERHi(T)

m(t)


D. J. Kim19


H(f) 와 HI(f) HQ(f) 간의 관계는 ?

또한

)tf2sin()t(s)tf2cos()t(s)t(s cQcI

)ff(S)ff(Sj2

1)ff(S)ff(S21)f(S

)f(H)ff(M)ff(M2A

)f(

cQcQcIcI

ccc

LPF

S

BPF

식

식

,

)cff(H)cff(H)f(IH

Wf)ff(H)ff(H)f(M2A

Wf),ff(S)ff(S)f(S

)f2f(S)f(Sj2

1)f2f(S)f(S21)ff(S

)f(S)f2f(Sj2

1)f(S)f2f(S21)ff(S

ccc

ccI

cQQcIIc

QcQIcIc

,

)cff(H)cff(Hj)f(QH

Wf)ff(H)ff(H)f(M2A

j

Wf)],ff(S)ff(S[j)f(S

ccc

ccQ


D. J. Kim20


SSB & VSB

fc

HI(f)

jHQ(f)

-fc fc

HI(f) : symmetric component

-fc fc

+jHQ(f)

component

symmetric-anti ; )ff(H)ff(H)f(jH ccQ


D. J. Kim21


3.6 Vestigial Side-Band Modulation

1. Filtering

1) fc를 중심으로 odd-symmetry

LSB(or USB) 의 vestige 만 보냄 .2) USB or LSB

0.5

0.5

1

1

f

f

fc+Wfcfc-fv

fc-W fc fc-fv

fc+fv

fc+fv

HI

HQ

HI

HQ


D. J. Kim22


2.Television Signals1)TV 신호의 특징

a)Video 신호가 large BW 대부분의 energy 가 low-frequency 에b) 수신기가 간단 , cheap use envelope detection

2) 주파수 특성

color

3.58 MHz


D. J. Kim23


3. 0.75 MHz (25%) 의 LSB 를 full scale 로 보내는 이유Envelope detection 에서 waveform distortion 을 줄이기

위해

1) Waveform distortion

add carrier component to apply envelope detector

Envelop detector output

2) m’(t) 에 의한 distortion 을 줄이는 방법a) ka를 줄인다 .

b) Vestigial sideband 의 폭을 늘인다 .

3) TV 신호에서의 해법a) 100% percentage modulationb) 0.75MHz 의 LSB

due to cheap

)tf2sin()t('mAk21)tf2cos()t(mk

211A)t(s ccacac

21

2

a

a

ac

21

2

a

2

ac

)t(mk211

)t('mk21

1)t(mk211A

)t('mk21)t(mk

211A)t(a

negligibledistortion


D. J. Kim24


3.7 SSB

1. 방법 : USB 나 LSB 만 전송

2. 이유 : Message m(t) 가 실수 M(f) 는 conjugate symmetric

3. 문제점 : LSB 나 USB 가 붙어 있을 경우 filtering 이 어렵다 .4. 적용분야 : Message spectrum 이 origin 에서 energy gap 이 있을 때

ex) Voice (-3400 ~ -300) (300 ~ 3400Hz)

)f(H

f


D. J. Kim25


5. Pass-band 에서 BPF 로 구현

BPF : highly selective filters ( 예 : Crystal resonator)

Multiple modulation 으로 구현

m(t) BPF

USB

ffc fc+W0

)tf2cos( c

-f1

f2

f1

-f2

0

f2+f1

easy BPF


D. J. Kim26


6. Time Domain Description of SSB (Baseband 에서 구현)

Hartley modulator

jH Q(f)

HI(f)

)fsgn(j)f(H, Q 즉

)tf2sin()t(m̂A21)tf2cos()t(mA

21)t(s

)tf2sin()t(m̂A21)tf2cos()t(mA

21)t(s

cccc

cccc

LSB

USB

H.T

-900

OSC

)tf2cos( c

)tf2sin( c

(t)m̂

m(t)

s(t)


D. J. Kim27


7. Demodulation of SSB signal1) 구현

2) Coherent detector : both in phase & in frequencya) Low-power 의 pilot carrier 를 전송b) Highly stable oscillator 사용 still phase error

3) Phase error 가 있을 경우

Phase distortionVoice insensitive to phase error Donald Duck voice effect

Music or Video unacceptable

-900

)tf2cos( c

)tf2sin( c

s(t)

(t)m̂

m(t)LPF

LPF

0f),jexp()f(M'AA41

0f),jexp()f(M'AA41

)f(V

)f(M)fsgn(j)f(M̂

sin)f(M̂cos)f(M'AA41)f(V

sin)t(m̂cos)t(m'AA41)t(v

cc

cc

0

cc0

cc0

여기서


D. J. Kim28


3.8 Frequency Translation

f3 = f2 + f1

f5 = f4 + f3= f4 (f2 f1)

= f4(f2-f1)

f4(f2+f1)

UpwardDownward

ex) f1= 0M f2= 44M f3 = 44M

f4= 66M f5 = 110M, 22M

ex) f1=110M f2= 1030M f3 = 920M, 1140M

f4= 876M f5 = 44M, 1796M

f6= 44M f7 = 0M, 88M

f3

f2 f4

f1 f5

TV

DTV


D. J. Kim29


3.9 Frequency-Division Multiplexing

ex2) Voice BW= 4kHz, SSBBasic Groups=12 Voice, fc=60+4nkHz. n=1~12

Super Groups= 5Basic Groups, fc=372+48nkHz. n=1~5

Master GroupVery Large Group

w1 w2 w3 wnf

w1

w2

wn

w1

w2

wn


D. J. Kim30


<HW #3> 3.4, 3.6, 3.8, 3.16, 3.21


D. J. Kim31


3.10 Angle Modulation

1. 장점 : better discrimination against noise and interference than AM

단점 : increased BW

2. Basic Definitions

1) PM

2) FM

dt)t(d

2)t(f

)]t(cos[A)t(s)t(

ii

ic

i

1 frequency ousinstantane

wavemodulated Anglem(t) of function a angle, : Let

signal, modulated-frequency

ysensitivitfrequency

t0fcc

t0fci

fc

dt)t(mk2tf2cosA)t(s

dt)t(mk2tf2)t(

)t(mkf)t(f i

signal, modulated-phase y sensitivit phase

)t(mktf2cosA)t(s

)t(mktf2)t(

pcc

pci


D. J. Kim32


3) AM 과 다른점a) AM 은 zero crossing 이 주기적 , PM 과 FM 은 비주기적b) AM 은 envelope 이 변화 , PM 과 FM 은 constant

carrier

m(t)

AM

PM

FM


D. J. Kim33


4) PM 과 FM 의 관계 : 미적분의 관계

4.11 Frequency Modulation

1. FM signal1) 특징 : nonlinear modulation

analysis is more difficult than AM


D. J. Kim34


2) FM signal

f - f :minff :max

deviation)frequency where

c

c

(Akf)tf2cos(ff

)tf2cos(Akf)t(f

mf

mc

mmfci

tf2tf2

tπf2)t(f

Δft)πf2(sintπf2

t)πf2(sinf

Δftπf2

dt)t(f2)t(

c

c

c

m

mc

mm

c

t0 ii

: min :max

angle the from angle the of departure maximum ;

index modulation ; where

phase

i

radian : FM band-wideradian : FM band-narrow

signal FM

11

)tf2sin(tf2cosA)t(s mcc

)tf2cos(Am(t) mm consider

frequency ousinstantane


D. J. Kim35


2. Narrow-Band Frequency Modulation1)

2) < BW of Narrow band FM > < BW of AM > = 2fm

3) 식 (1) 의 구현

tff2costff2cosA21tf2cosA)t(s

tff2costff2cosA21tf2cosA

)tf2sin(tf2sinAtf2cosA)t(s)tf2sin()tf2sin(sin

1)tf2sin(cos

)tf2sin(sintf2sinA)tf2sin(costf2cosA)tf2sin(tf2cosA)t(s

mmccccAM

mmccc

mcccc

mm

m

mccmcc

mcc

case AM

)18057( radians. 1 : Band-Narrow

0

π

(1)

(2)

(3)


D. J. Kim36


4) (2) (3) 식의 그림상에서 비교문제 : envelope 이 변한다

0.3 radians negligible

3. Wide-band FM1) FM wave

m

mc

c

mcc

ftstf2jAts

tf2jtstf2jtf2jAts

withfunctionperiodic : where

)(~sinexp)(~

exp)(~ResinexpRe)(


D. J. Kim37


FM wave

-nnc

n

n

)exp(JA(t)s

J 21)(J

kind first the of function Bessel order nth

xlet

where

series Fouriercomplex by Expand

tnf2j~)(Ac

dxnxxsinjexp

dxnxxsinjexp2Ac

tf2

dttnf2jtf2sinjexpAf

dttnf2jexp)t(s~fc

tnf2jexpc)t(s~

)t(s~

m

cn

cn

m

mmf21

f21cm

mf21

f21mn

nmn

m

m

m

m

nmcnc

nmcnc

tnff2cos)(JA

tnff2jexp)(JReA)t(s

mcmcnn

c nfffnfff)(J2A

)f(S

T.F


D. J. Kim38


)(J)(J)(J)(J

nn

nn

n all for )(J)1()(J nn

n

2n,02

)(J

)(J

1)(J

n

1

0

n

2n 1)(J

2) Properties of Bessel function. a) For n even For n odd

b) For n odd

c)


D. J. Kim39


3) Observations.a) Spectrum, fcnfm, n=0,1,2,…...

b) for small , spectrum at fc, fm narrow-band FM

c) Amplitude of carrier component J0() varies with

example 3.Fixed freq (fm) & varying amplitude (i, e, f)

Varing freq(fm) & fixed amplitude (i, e, f)

2

cn

2

n

2

c A21)(JA

21P

index moduiation : mff


D. J. Kim40


4. Transmission Bandwidth of FM signals.

1) BW of FM 의 개념 .실제 FM: infinite number of side freq.Effectively finite number of side freq.Single tone FM case.

Narrow band : BW order of 2fm

Wide band : BW order of 2f

2) Carson’s ruleApproximate BW of FM by single tone fm

3) BW of FM the separation between the two freq beyond which none of the frequencies is greater

than 1% of the unmodulated carrier amplitude

= 2nmax fm

where nmax=largest value of integer n that satisfies the requirement

m

mT

f)1(2

11f2f2f2B

def

01.0)(J n

2nmax

Carson’s rule

0.1 0.3 0.5 1.0 2.0 5.0 10.0 20.0 30.0 2 4 4 6 8 16 28 50 70

2.2 2.6 3 4 6 12 22 42 62


D. J. Kim41


Universal curve

4) General caseHighest frequency W worst case tone fm

Deviation ratio D : maximum possible amplitude

Ex4) FM radio in US f=75KHz W= 15KHz D= 75 / 15 = 5By carson’s rule BT=2(75+15)=180KHz

By universal curve BT= 3.275=240KHz

정결서에이사 curve universal

rule sCarson’

200KHz 사용

mTT

T ff

Bf

fB

B )()(


D. J. Kim42


5. Genetation of FM signals1) Indirect FM

a) Crystal controlled OSC : to provide frequency stability

b) Frequency multiplier

c) 식 .

t

0fcc

nn

33

221

t

0fcc

dt)t(mnk2tnf2cos'A)t('s

)t(sa......)t(sa)t(sa)t(sa)t(v

dt)t(mk2tf2cosA)t(s


D. J. Kim43


d) Freq. Multiplier 2 개를 사용한 예

Ex5). ( 목적 ) fc=100MHz, minimum of f = 75kHz m(t) : 100Hz~15KHz audiof1=0.1MHz, 1=0.2 radians.

100Hz f1=20Hz

15KHz f1=3KHz

To make minimum f=75KHz

By solving & n1=75

n2=50

2) Direct FM a) FM fi(t)=fc+kfm(t)

VCO 로 구성 (voltage controlled oscillator)

VCO fi(t)=fc+ kfm(t)m(t)

21

2112c

1

nn1059100nfnff

375020

75000Hz20f

f

..

min

nn 21

그리고


D. J. Kim44


b) Oscillator 의 구현 예

c(t) : (varactor or varicap) + fixed capacitance

ex) p-n junction diode in reverse biasthe larger the reverse voltage the smaller the capacitance

c) VCO 를 이용한 wide-band FM

00

m0i

m0

0

021

0

21

m0

0i

m0

21

i

ff

c2c

tf2fftf

tf2c2c1f

cLL21tf

tf2c

c1ftf

tf2cctc

tcLL21tf

where

where

cos)(

cos)(

cos)(

cos)()(

)(


D. J. Kim45


d) VCO 를 이용한 FM 에서 주파수 안정화를 위한 feedback scheme

가정 m(t) is zero mean LPF 는 f0 만 control 할 수 있도록 Narrow-band 로 구현

(m(t) 의 BW 에 비해 Narrow 하게 )

6. Demodulation of FM signals1) Direct Method frequency discriminator

= slope circuit + envelope detector

slope circuit

otherwise , 0

2Bff

2Bf,

2Bffa2j

2Bff

2Bf,

2Bffa2j

)f(H Tc

Tc

Tc

Tc

Tc

Tc

1


D. J. Kim46


t0fc

T

fcT

c1

t0f

T

fcT

T1

TTT

11

TTT

1

t0fc

t0fcc

2dt)t(mk2tf2cos)t(m

Bk2

1aAB

)tf2jexp()t(s~Re)t(s

dt)t(mk2jexp)t(mBk2

1aABj

)t(s~Bjdt

)t(s~da)t(s~

02

Bf

2B

)f(S~2

Bfa2j

)f(S~)f(H~21)f(S~

02

Bf

2B

2B

fa4j)f(H~

dt)t(mk2jexpA)t(s~s(t)

dt)t(mk2tf2cosA)t(s

otherwise ,

,

otherwise

of envelopecomplex

s(t) s2(t)

s1(t)

so(t)

)(~ ts1

)(~ ts2

< Balanced frequency discriminator >


D. J. Kim47


)()(~

)(

tmBk2

1aABts

1tmBk2

T

fcT1

T

f

detector envelope usemay wet, all for If

)t(maAk4)t(s~)t(s~)t(s

)t(mBk2

1aAB)t(s~

)f(H~)f(H~

cf210

T

fcT2

12


D. J. Kim48


2) Circuit diagram 으로 구현

각각의 Resonator 의 3-dB BW=2B 일 때 3B separation 이 ideal.

위 회로의 distortion factora) s(t) 의 spectrum 이 BW=BT밖에서 완전히 0 이 아니다 .

b) Tuned filter 가 완전히 band limit 되어 있지 않다 .c) Tuned filter 특성이 모든 FM 대역에서 완전히 linear 하지 않다

cycle per dissipatedenergy cycle one during circuit the in storedenergy Maximum2

circuit RLC for BW 3dB

)(f freq. Resonantfactor Q c


D. J. Kim49


7. FM Stereo Multiplexing1) FM stereo 의 조건

a) The Tx has to operate within the allocated FM channelsb) Compatible with monophonic radio receivers

2) Multiplexed signalm(t)=[ml(t)+mr(t)]+[ml(t)-mr(t)]cos(4fct)+Kcos(2 fct) where fc=19KHz

pilot=19KHz: 8~9% of the peak freq. deviation. ml+mr or ml-mr : DSB-SC

3) 구조


D. J. Kim50


3.12 PLL

1. 용도 : Synchronization, frequency division / multiplicationindirect frequency demodulation.

2. PLL 의 구조

Locking 조건

다른 응용 : Coherent detection 용 clock generation

t

0v2

2cv

t

0f1

1cc

dt)t(vk2)t(where

)t(tf2cosA)t(r

dt)t(mk2)t(where

)t(tf2sinA)t(s

90 Phase

0차이는

동일주파수

v

f21 k

k)t(m)t(v)t()t(if


D. J. Kim51


3. Nonlinear Model of PLL

여기서 sin( ) : nonlinear function difficult to analyze

4. Linear Model of the PLLNear phase-lock : 즉 e(t)<0.5 radians.

sin[e(t)] e(t)

parameter gain-loop : k where

filter loop : e wher

gain multiplier; here W

0 vcvm

e01e

t

0v1

21e

m

evcm

AAkk

d)t(h)(sinK2dt

)t(ddt

)t(d)t(h)t(h)t(e)t(v

dt)t(vk2)t(

)t()t()t(k

)t(sinAAk)t(e

dt

tdthtK2

dttd 1

e0e )(

)()()(


D. J. Kim52


BW of h(t)=BW of m(t)

PLL of function transfer loop-open ; wherejf

)f(HKL(f)

)f()f(L1

1)f(

0

1e

)t(mkk

dt)f(d

k21)t(v

)f(kjf)f(V1)f(LIf

)f()f(L1

)f(Lkjf

)f()f(Lkjf)f()f(H

kK

)f(V

v

f1

v

1v

1v

ev

ev

0

output

1(t) dtd

v(t)

vk21


D. J. Kim53


5. PLL 의 BW 와 Lock Range

1) 1st-order H(s)=1

2) 2nd-order

)()(

)()(

)()()(

)()(

)(

)()(

)()(

)(

sHKssHK

ss

s21sHK2ss

K2KssHKs

ss

jffHKfL

ffL1

1f

L

L

1

2

Le2

0L1L

e

0

1e

where

RadianBW

W Range Lock

stable

0

L

L

L

L

L

1

2

K

K

0K

KsK

ss

)()(

)s()s(log20

1

2

LKlog )log(

decade/dB20

2

1

KsKs

sH

)(

0K, KKK

KKsKKsKKsK

ss

KK

K0HKw

1LL2

1L2L2

1LL

1

2

2

1LL

if stable

Range Lock

)()(

)(


D. J. Kim54


(a) |z| < |p|

(b) |z| = |p|

즉 BW 과 Lock Range 을 별도 조절 가능

Computer Experiment II Acquisition Mode

a) acquisition tracking

1L KK

2

1L K

KK

best 0.707 0.125Hz of step freq a for

이

0.1,707.0,3.0

Hz21f,Hz

250K n0

)()(

logss

201

2

)wlog(1Klog

1L KKlog

1L KKlog1L KKlog

1Klog


D. J. Kim55


(a)

(d)(c)

(b)

32f)d(

127f)c(5.0f)b(Hz325.0f)a(

(b), (c), (d) 의 경우 Cycle slipping : Phase error of 2 radians a slip by one cycle

b) Variations in the instantaneous frequency of the PLL’s VCO for varying frequency step f.


D. J. Kim56


3.13 Nonlinear Effect in FM system

1. Nonlinearties1) Strong nonlinearity : square-law modulators, limiters, frequency multiplier2) Weak nonlinearity : due to imperfections.

2. Weak Nonlinearity 의 경우

( 결론 ) FM 은 Channel 로 전송 중 생기는 Amplitude Nonlinearity 에 의한 영향이 없다 . Microwave radio, satellite communication system 에 사용 .이 채널에서는 highly nonlinear Amp 와 power transmitter 를 사용한다 왜냐하면 maximum power 을 내는 것이 중요하기 때문 .( 단점 ) Extremely sensitive to phase nonlinearities

wffwffwff

ttfAa

ttfAattfAaAaAatv

dttmktttfAtvtvatvatvatv

c

cc

cc

cccccc

t

f

cci

iii

23 22

)(36cos41

)(24cos21)(2cos

43

21)(

)(2)( where

)(2cos)( input)()()()(

3

3

2

2

3

31

2

20

0

3

3210

2

조건주파수

)(cos)( ttf2Aa43Aatv c

3c3c1

w2f2BWff0 c


D. J. Kim57


3.14. The Superheterodyne Receiver

1. Tasks of receiver1) Carrier-frequency tuning2) Filtering3) Amplification

2. Superheterodyne : RF IFDetection(Demodulation)

<HW #4> 3.28, 3.30, 3.45

757.25Mch69

11.25M

ch2 LO

Tuning Channel 44MHzIF

801.25806~800

ch69

55.2560~54

ch2 RF ;TV ex)

FRLOLORFIFfforfff

BPF1 BPF2 LPF 50~860M LO 44M

44M 55.25 - 11.25 = 44image frequency 37.25 + 11.25 = 44

IF

LO

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