111 Communications Fall 2008 NCTU EE Tzu-Hsien Sang

22 Outlines Linear Modulation Angle Modulation Interference Feedback Demodulators Analog Pulse Modulation Delta Modulation and PCM Multiplexing 2

3 Phase-Lock Loops (PLL) for FM Demodulation Tracks the instantaneous angle (phase and frequency) of the input signal. (1) phase detector (comparator) (2) loop filter (3) loop amplifier (4) VCO (voltage-controlled oscillator)

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6 Analysis of PLL: first, simplification, of course. Assume that the frequency matches, look at the phase difference. (1) Non-linear Model:

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8 Now we will present classical PLL analysis with classification on different loop filters. Loop filter = 1

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15 First-order PLL summary 1.Limited lock range 2.Nonzero steady state error 3.The complete system loop gain is 4.K t also controls the bandwidth of PLL 5.A large K t is impractical since (a) hardware implementation issues and (b) noise increases due to the wide bandwidth. To overcome some of the drawbacks, move to higher-order PLL.

16 Perfect 2 nd -order PLL Use the linear model to analyze.

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20 Applications of PLL (1) Frequency multiplier: Generate the harmonics of the input and the VCO tracks one of the harmonics.

21 (2) Frequency divider: Generate the harmonics of the VCO output. One of the harmonics tracks the input.

22 (3) FM demodulator Implementation of the phase detector: