Introduction to Communication Systems 4

EEE 330Introduction to

Communication Systems

Lecture # 4

Angle Modulation and Demodulation

Overview

� The Objectives of Today’s Lecture is to introduce angle (or exponential) modulation

� Analog Angle modulation is a non-linear modulation technique that maps the message signal to the angle of a transmitted carrier

� There are two basic forms:

� Phase Modulation (PM)

� Frequency Modulation (FM)

� Read Carlson et al, Chapter 5, Lathi 4.1 –4.8

Analog Angle Modulation

PM and FM

� There are two basic forms of angle modulation� 3Frequency Modulation (FM)

� 3 Phase Modulation (PM)

� 3FM – the frequency of the carrier is varied linearly with the message signal

� 3PM – the phase of the carrier is variedlinearly with the message signal

Frequency Modulation

FM

Phase Modulation

Non-linear Nature of Angle Modulation

Non-linear modulation – cont.

Transmitted Signals for Angle Modulation

Instantaneous Frequency

Description of Frequency Modulation

FM vs. AM

Comparison of PM and FM: Example #1

Comparison of PM and FM: Example #2

FM signal shows continuous frequency increasePM signal has single frequency shift

Comparison of PM and FM: Example #3 Frequency change for FM

Phase change for PM

Comparison of PM and FM: Example #4

Equivalency of Frequency Modulation and Phase Modulation

Comparison of FM and PM

� They are very similar in signal structure

� Both allow designer to trade bandwidth for power efficiency

� FM has advantages in:� Ease of implementation� Performance in noise� Larger range of BW/performance trade-off

� FM is used almost exclusively

FM – Tone Modulation

Sinusoidal Message Signal (Tone Modulation)

Narrowband FM (NBFM)

NBFM

Resulting Distortion

NBFM Approximation

NBFM Approximation

Wideband FM – Tone modulation

WBFM - Tone modulation

Spectrum of Tone Modulation

Narrowband vs. Wideband FM

Spectrum

Spectrum

NBFM vs. WBFM

Example

Example- Cont.

Example- Cont.

Example- Cont.

Bandwidth

Example- Cont.

Bandwidth

Carson’s Rule – General Signals

Generation and Demodulation of FM Signals

Generation of NBFM

Generation of WBFM

Generation of WBFM – Direct Method

Generation of WBFM – Indirect Method

Generation of WBFM – Indirect Method

Demodulators for FM Signals

Practical Demodulators

Frequency Discriminator

Frequency Discriminator

Taking Derivative

Balanced Frequency Discriminator

Balanced Frequency Discriminator

Phased-Locked Loop (PLL)

PLL

PLL

Zero-crossing Detector