ch3.4pll

ch3.4pll - 1 EEN 404 Communication Systems Ch3.4...

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1 EEN 404 EEN 404 Communication Systems Communication Systems Ch3.4 Phase Ch3.4 Phase - - Locked Loop Locked Loop
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2 Example: phase noise, e.g., for DSB modulation If there is a phase error, then after lowpass filtering and amplitude scaling What happened if is time-varying PLL: generate an output signal that has a fixed relation to the phase of the input signal Phase Phase - - Locked Loop (PLL) Locked Loop (PLL) • demodulation of angle modulated signal • carrier and symbol synchronization • frequency synthesis •etc. PLL can be employed to estimate the phase
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3 Phase-locked loop (PLL) X lowpass Phase detector: inverter K d : a constant
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4 VCO: voltage-controlled oscillator is a frequency modulator (frequency deviation of the output is proportional to the input signal) K v : VCO constant, or frequency sensitivity Objective of PLL: to generate a VCO output e 0 (t) which has the same phase angle (t) as the input signal’s phase (t).
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5 Figure 3-46 Nonlinear PLL model Assume the transfer function of the loop filter is F(f)=1 :
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ch3.4pll - 1 EEN 404 Communication Systems Ch3.4...

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