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ECE4371_class5 - ECE 4371 Fall 2009 Zhu Han Department of...

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ECE 4371, Fall, 2009 Zhu Han Department of Electrical and Computer Engineering Class 5 Sep. 8 th , 2007
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Phase-Locked Loop Phase-Locked Loop Can be a whole course. The most important part of receiver. Definition: a closed-loop feedback control system that generates and outputs a signal in relation to the frequency and phase of an input ("reference") signal A phase-locked loop circuit responds both to the frequency and phase of the input signals, automatically raising or lowering the frequency of a controlled oscillator until it is matched to the reference in both frequency and phase.
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Ideal Model Ideal Model Model Si=Acos(w c t+ φ 1 (t)), Sv=A v cos(w c t+ φ c (t)) Sp=0.5AA v [sin(2w c t+ φ 1 + φ c )+sin( φ 1 - φ c )] So=0.5AA v sin( φ 1 - φ c )=AA v ( φ 1 - φ c ) Capture Range and Lock Range LPF VCO
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Type of waves Type of waves
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GPS Orbits GPS Orbits
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FM Basics FM Basics VHF (30M-300M) high-fidelity broadcast Wideband FM, (FM TV), narrow band FM (two-way radio) 1933 FM and angle modulation proposed by Armstrong, but success by 1949. Digital: Frequency Shift Key (FSK), Phase Shift Key (BPSK, QPSK, 8PSK,…) AM/FM: Transverse wave/Longitudinal wave
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Angle Modulation vs. AM Angle Modulation vs. AM Summarize: properties of amplitude modulation Amplitude modulation is linear just move to new frequency band, spectrum shape does not change.  No new frequencies generated. Spectrum: S(f) is a translated version of M(f) Bandwidth ≤ 2W Properties of angle modulation They are nonlinear spectrum shape does change, new frequencies generated. S(f) is not just a translated version of M(f) Bandwidth is usually much larger than 2W
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Angle Modulation Pro/Con Application Angle Modulation Pro/Con Application Why need angle modulation? Better noise reduction Improved system fidelity Disadvantages Low bandwidth efficiency Complex implementations Applications FM radio broadcast TV sound signal Two-way mobile radio Cellular radio Microwave and satellite communications
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Instantaneous Frequency Instantaneous Frequency [ ] ( ) cos ( ) , where :carrier amplitude, ( ) :angle (phase) c i c i s t A t A t θ θ = ( ) 1 ( ) 2 i i d t f t dt θ π =
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