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© 2007 Texas Instruments Inc,

Content developed in partnership with Tel-Aviv University

From MATLAB® and Simulink® to Real Time with TI DSPs

Amplitude Modulation

Slide Slide 22© © 2007 Texas Instruments Inc, 2007 Texas Instruments Inc,

Amplitude Modulation

• Amplitude Modulation is a process where the amplitude of a carrier signal is altered according to information in a message signal.

• The frequency of the carrier signal is usually much greater than the highest frequency of the input message signal.

Slide Slide 44© © 2007 Texas Instruments Inc, 2007 Texas Instruments Inc,

AM – Basic Definitions (cont.)

The Envelope:

The AM Signal

ttmkAts cc cos 1

tmkAts c 1

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2-5

-4

-3

-2

-1

0

1

2

3

4

5

Slide Slide 55© © 2007 Texas Instruments Inc, 2007 Texas Instruments Inc,

The AM Spectrum

0 500 1000 1500 2000 2500 3000 3500 4000 4500 50000

0.5

1

1.5

Frequency (Hz)

|M(f

)|

0 500 1000 1500 2000 2500 3000 3500 4000 4500 50000

0.5

1

1.5

Frequency (Hz)

|Y(f

)|

tm ts

Carrier

Side Bands

Slide Slide 66© © 2007 Texas Instruments Inc, 2007 Texas Instruments Inc,

AM Modulation Scheme

tA cc cos k

1

tm ts+ Xk

Slide Slide 77© © 2007 Texas Instruments Inc, 2007 Texas Instruments Inc,

Square-Law Demodulation

2

ttmkAtmkA

ttmkAts

ccc

cc

21515

12222

22

cos..

cos

LPF ts

offset

c

DCtm

tmkAty

125.

22 15 tmkAc .

ty

Slide Slide 88© © 2007 Texas Instruments Inc, 2007 Texas Instruments Inc,

Coeherent Demodulation

tccos

ttmkAtmkA

ttmkA

ttmkA

tttmkAts

ccc

cc

cc

ccc

2cos15.15.

2

2cos11

cos1

coscos12

LPF ts

offset

c

DCtm

tmkAty

15.

tyX

Slide Slide 99© © 2007 Texas Instruments Inc, 2007 Texas Instruments Inc,

Hands-On

• Simulation

• Implementation using the DSK6713

Slide Slide 1010© © 2007 Texas Instruments Inc, 2007 Texas Instruments Inc,

The Simulation Environment

Modulator

VirtualScope

DemodulatorInformation

Signal

Demodulated

Signal

Slide Slide 1111© © 2007 Texas Instruments Inc, 2007 Texas Instruments Inc,

The Simulation Environment

Slide Slide 1212© © 2007 Texas Instruments Inc, 2007 Texas Instruments Inc,

Real Time Environment

DSK6713

CODEC

TMS320C6713

AMModulator

D/A(Left)

AMDemodulator

A/D(Left)

A/D(Right)

D/A(Right)

ts

ty

Line In

Line In

Line Out

Line Out

Signal Generator

Scope

PCRTDX

Slide Slide 1313© © 2007 Texas Instruments Inc, 2007 Texas Instruments Inc,

GUI

Slide Slide 1414© © 2007 Texas Instruments Inc, 2007 Texas Instruments Inc,

SQRT Detector – Real Time

Slide Slide 1515© © 2007 Texas Instruments Inc, 2007 Texas Instruments Inc,

Coherent Detection – Real Time

Slide Slide 1616© © 2007 Texas Instruments Inc, 2007 Texas Instruments Inc,

Configurable Carrier

nf

fj

s

csc

s

c

enf

fnT

2

Re2coscos

nf

fj

s

csc

s

c

enf

fnT

2

Re2coscos