lecture6

# lecture6 - EEE455/591 EEE455/591 Fre ncy and...

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EEE455/591 Frequency and Phase Modulation FM and PM Reading: Textbook Sections 3.3, skip 3.3.2 Topics: 1. 1. What is FM and PM? Why? What Applications? 2. 2. Mathematical Description of PM and FM 3. 3. Spectrum Usage of FM and PM 4. 4. Practical Implementations of FM

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1. FM and PM: What and Why? Angle Modulation: Transmit the message in: - the frequency f c of the carrier (FM), or - the phase θ c of the carrier (PM) - but not the A c amplitude of the carrier (AM)! Use extensively in: - FM radio (e.g. KNIX 102.5MHz) - Audio part of TV broadcasting - First generation analog cellular phones (Narrowband FM) Result: Constant envelope modulated signal: ) 2 cos( ) ( c c c t f A t u θ π + =
1. FM and PM: Why? Advantages: Improved noise immunity Power efficient when amplifiers operates in saturation Immune to distortion in amplitude. Disadvantages: Takes more bandwidth than AM More complex transceivers. Frequency Modulation: The message modulates the frequency of the carrier: Phase Modulation: The message modulates the phase of the carrier. ) 2 cos( ) ( c c c t f A t u θ π + =

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2. Representation of PM and FM in Time Phase Modulation (PM) Frequency Modulation (FM) )) ( 2 cos( ) ( t m k t f A t u p c c + = π ) ) ( 2 cos( ) ( τ d m k t f A t u t f c c - + =
2. “Instantaneous” Frequency of PM and FM Definition of instantaneous frequency: PM: Maximum phase deviation FM: Maximum frequency deviation Modulation Index PM: FM: For message bandwidth W )) ( 2 cos( )) ( cos( ) ( t t f A t A t u c c c φ π θ + = = ) ( ' 2 1 ) ( 2 1 ) ( t f dt t d t f c i + = = | ) ( | max max t m k p = ∆φ | ) ( | max max t m k f f = max | ) ( | max β = = t m k p p W f W t m k f f max | ) ( | max = =

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2. Relationship Between AM and FM FM: PM: )) ( 2 cos( ) ( t m k t f A t u p c c + = π ) ) ( 2 cos( ) ( τ d m k t f A t u t f c c - + =
2. Equivalence of PM and FM

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## This note was uploaded on 11/01/2009 for the course EEE 455 taught by Professor Hui during the Spring '09 term at ASU.

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lecture6 - EEE455/591 EEE455/591 Fre ncy and...

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