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