Double Side Band Suppressed Carrier - GUCeee.guc.edu.eg/Courses/Communications/COMM601... · Dr....

Dr. Ahmed El-Mahdy COMM 601: Modulation I

COMM 601: Modulation I

Lecture 4

Double Side Band Suppressed Carrier

Dr. Ahmed El-Mahdy COMM 601: Modulation I

Double Side Band (DSB)

Compare between this equation and the equation of

conventional AM

Dr. Ahmed El-Mahdy COMM 601: Modulation I

3

0 0.05 0.1 0.15 0.2 0.25

-20

0

20

Time[Sec.]

Sc(t

)

0 0.05 0.1 0.15 0.2 0.25

-20

0

20

Time[Sec.]

m(t

)

0 0.05 0.1 0.15 0.2 0.25

-20

0

20

Time[Sec.]

SD

SB

(t)

CARRIER SIGNAL

MODULATING BASEBAND SIGNAL

DOUBLE SIDEBAND MODULATED SIGNAL

Dr. Ahmed El-Mahdy COMM 601: Modulation I

4

0 0.02 0.04 0.06 0.08 0.1 0.12

-25

-20

-15

-10

-5

0

5

10

15

20

25

Time[Sec.]

SD

SB

(t)

DOUBLE SIDEBAND MODULATED SIGNAL

Phase Reversal

Dr. Ahmed El-Mahdy COMM 601: Modulation I

Phase Reversal in DSB

Dr. Ahmed El-Mahdy COMM 601: Modulation I

DSB Spectrum

Dr. Ahmed El-Mahdy COMM 601: Modulation I

tfatm mm 2cos

tfftffa

ts mcmcm 2cos2cos2

tftfats mcm 2cos2cos

mcmcm

mcmcm

ffffffa

ffffffa

fS

2

1

2

1

2

2

1

2

1

2

mmm ffff

afM

2

MODULATING SIGNAL

MODULATED (DSB) SIGNAL

DSB Spectrum for Sinusoidal Modulating Signal

Dr. Ahmed El-Mahdy COMM 601: Modulation I

8

0 0.05 0.1

-20

-10

0

10

20

Time[Sec.]

m(t

)

0 0.05 0.1

-20

-10

0

10

20

Time[Sec.]

m(t

)

0 50 100 150 200 2500

2

4

6

Frequency[Hz]

M(f

)

0 50 100 150 200 2500

2

4

6

Frequency[Hz]

SD

SB

(f)

MODULATING SIGNAL MODULATED (DSB) SIGNAL

Hzf

Hzf

va

c

m

m

200

10

10

UPPER SIDEBAND

(USB)

LOWER SIDEBAND

(LSB)

Dr. Ahmed El-Mahdy COMM 601: Modulation I

tftmAts cc 2cos)(

tfjcetCts

2Re

tfj

ccetmAts

2)(Re

)(tmAtC c

)(tmAta c

INSTANTANEOUS

AMPLITUDE

INSTANTANEOUS

PHASE

)(tmAt c

INSTANTANEOUS

FREQUENCY

tdt

dtf

2

1

Instantaneous Amplitude, Phase, and Frequency of DSB

Dr. Ahmed El-Mahdy COMM 601: Modulation I

tftfats cmm 2cos2cos

tfj cetCts2

Re

tfj

mmcetfats

22cosRe

tfatC mm 2cos

tfata mm 2cos

INSTANTANEOUS

AMPLITUDE

INSTANTANEOUS

PHASE

02cos

02cos0

2cos

tf

tf

tfat

m

m

mm

INSTANTANEOUS

FREQUENCY

tdt

dtf

2

1

1cAAsume

Instantaneous Amplitude, Phase, and Frequency of DSB(single Tone)

Dr. Ahmed El-Mahdy COMM 601: Modulation I

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16

-20

0

20

Time[Sec.]

XD

SB

(t)

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16

-20

0

20

Time[Sec.]

XD

SB

(t)

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16

-20

0

20

Time[Sec.]

a(t

)

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16-200

0

200

Time[Sec.]

phai(t)

MODULATING SIGNAL

MODULATED (DSB) SIGNAL

INSTANTANEOUS AMPLITUDE

INSTANTANEOUS PHASE

Dr. Ahmed El-Mahdy COMM 601: Modulation I

Transmitted Power of DSB

)()(signalDSB of envelopeComplex tmAtC c

)(2

)(2

1

22

2

tmA

tCP

c

avg

22

2

2

])([max2

])([max2

1

)(max2

1

tmA

tmA

tCP

c

c

PEP

Using Complex Envelope

Dr. Ahmed El-Mahdy COMM 601: Modulation I

Calculation of Transmitted Power of DSB using power spectrum

Sp(f)

fc -fc

f 4

2

cA

Power Spectrum

)(2

)()(4

)()(4

)(

:then2 than lessmuch contentsfrequency with signal baseband a is m(t) If

22

222

2

c

tmA

tmtmA

dfffMffMA

dffSP

f

c

c

ccc

pavg

)(2 tm

Dr. Ahmed El-Mahdy COMM 601: Modulation I

Generation of DSB

Dr. Ahmed El-Mahdy COMM 601: Modulation I

Generation of DSB

(a)Block diagram of the product modulator

(b)Baseband signal (modulating signal) (c) DSB

modulated signal

(1) Product Modulator

Dr. Ahmed El-Mahdy COMM 601: Modulation I

Generation of DSB (Cont.) (2) Balanced Modulator

s

Dr. Ahmed El-Mahdy COMM 601: Modulation I

Coherent Demodulation of DSB

S(t)

Dr. Ahmed El-Mahdy COMM 601: Modulation I

Coherent Demodulation of DSB (Cont.)

S(f)

Dr. Ahmed El-Mahdy COMM 601: Modulation I

Effect of Phase Error on Coherent Demodulation of DSB

S(t)

Dr. Ahmed El-Mahdy COMM 601: Modulation I

Remarks on DSB Coherent demodulation

Phase Locked Loop

Dr. Ahmed El-Mahdy COMM 601: Modulation I

Squaring Loop

S(t)

Dr. Ahmed El-Mahdy COMM 601: Modulation I

Voltage Controlled Oscillator (VCO)

If the control signal is negative, then the VCO phase increases.

If the control signal is positive, then the VCO phase decreases.

Dr. Ahmed El-Mahdy COMM 601: Modulation I

Voltage Controlled Oscillator (VCO)

Dr. Ahmed El-Mahdy COMM 601: Modulation I

Costas Phase Locked Loop

_

_

_

Dr. Ahmed El-Mahdy COMM 601: Modulation I

Explanation of Costas Phase Locked Loop

Dr. Ahmed El-Mahdy COMM 601: Modulation I

Explanation of Costas Phase Locked Loop

_

_

_

_

_

)]4sin())sin(()[(2

1

)]4sin())()[sin((2

1

)]4sin())[sin((2

1

0

0

0

cvcvcc

cvcvcc

cvccvc

tftmAA

tftmAA

tftmAA

Dr. Ahmed El-Mahdy COMM 601: Modulation I

Explanation of Costas Phase Locked Loop It has cut off

freq. near zero.

It acts as

integrator to

produce DC

control voltage

to VCO

_

Dr. Ahmed El-Mahdy COMM 601: Modulation I

Phase Locked Loop (PLL)

S(t) LPF Filter

H(f)

)]4sin()[sin(2

1)( 000 icic tfAAtx

)][sin(2

1)][sin(

2

1)( 0000 ecic AAAAte

Phase Shift 90

Dr. Ahmed El-Mahdy COMM 601: Modulation I

Notes: Phase Locked Loop (PLL) Note that the PLL is locked -90 degree out of phase with

respect to the incoming signal. Then the output of the PLL

needs to be shifted by 90 degree so that it will be in phase

with the carrier of the input signal.

Dr. Ahmed El-Mahdy COMM 601: Modulation I

PLL Can Track Phase or Frequency

Dr. Ahmed El-Mahdy COMM 601: Modulation I

Conventional AM versus DSB

Dr. Ahmed El-Mahdy COMM 601: Modulation I

Remember: Bandwidth of AM & DSB