ECE264D_Lecture3

ECE264D_Lecture3 - Design of CMOS RF Frequency Synthesizers...

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Design of CMOS RF Frequency Synthesizers ecture 3 : Charge Pump PLL Lecture 3 : Charge Pump PLL GANG ZHANG September 2009 © 2009 G. Zhang ECE264D Fall 2009
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! Recall XOR or Multiplier phase detector ! can only detect phase, only work with two inputs with same/close frequencies; ! PFD can detect both phase and frequency ! Works with charge pump, “THE” only phase frequency detector used in analog PLL in RF applications. ! A state machine; Phase and Frequency Detector UP Page 2 ECE264D RF Frequency Synthesizers © 2009 G. Zhang DFF Reset D Q DFF Reset D Q FREF V dd V dd NDIV DN
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PFD state machine diagram DFF Reset D Q DFF Reset D Q Fref V dd V dd Ndiv UP DN fref ndiv UP DN fref ndiv UP DN Page 3 ! Sequential phase detectors: ! Decision depends on the sequence of events(rising edges) ! May make wrong decision when miss edge ! Has “dead zone”: when input phase error is very small, real circuit can’t respond in time; ECE264D RF Frequency Synthesizers © 2009 G. Zhang Reset Reset Fref leads Ndiv Fref lags Ndiv
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Charge pump UP DN To loop filter Icp Icp UP DN net Net charge = Icp* t t Page 4 ! Convert phase info from PFD to charge output: the heart of PLL ! Small-signal time-invariant model: ECE264D RF Frequency Synthesizers © 2009 G. Zhang Average charge pump output current: Corresponding charge pump gain: (A/radian)
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Charge pump: Dead Zone UP DN Icp Icp fref
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ECE264D_Lecture3 - Design of CMOS RF Frequency Synthesizers...

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