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A Low Spur Fractional-N Frequency Synthesizer Architecture

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									A Low Spur Fractional-N Frequency
     Synthesizer Architecture

  Circuits and Systems, 2005. ISCAS 2005. IEEE International Symposium on
                  23-26 May 2005 Page(s):2807 - 2810 Vol. 3



              指導教授 : 林志明 教授
                 學生 : 黃世一

                                                                        1
Outline
   Abstract
   Introduction
   Fractional spurs
   Blocking of the fractional spurs
   Simulation results
   Conclusions
   References
                                       2
    Abstract
   New architecture of a fractional-N PLL
    frequency synthesizer

   Loop filter with a discrete time comb filter

   Loop filter architecture can be efficiently
    implemented using switched capacitor
    techniques
                                                   3
     Introduction 1
   Fractional-N PLL, Better phase noise
    performance, faster lock and better spur
    levels

   Advantages: larger loop bandwidth, better
    VCO phase noise suppression, faster lock
    time and higher PFD update frequencies

   Fractional spurs and cycle slipping         4
    Introduction 2
   Delta-sigma control in the feedback divider

   Fractional spurs by the delta-sigma
    modulator to high frequencies.

   Delta-sigma modulator can generate spurs

   Pseudorandom sequences                    5
    Introduction 3
   Another way to suppress fractional spurs is
    to reduce the bandwidth of the PLL

   Degradation of the noise performance,
    lock time and jitter



                                              6
    Introduction 3
   Extension of the conventional fractional-N
    technique

   A discrete-time loop filter with notches at
    spur frequencies

   A low power frequency synthesizer design
    with low spur levels
                                                  7
     Fractional spurs
   Fractional-N frequency synthesizers
    generate spurs at the output of VCO



                        K  N  1  M  K   N     K
                   Nf                             N
                                    M                  M




                                                           8
   ωs = 2πfs
   fs - frequency of a spur
   Vi - amplitude of the i-th harmonic
   ϕi - phase of the i-th harmonic
                                          9
   ω0 = 2πf0
   f0 - frequency of the free running oscillator
   VA - amplitude of oscillation
   Φ(t) - phase of the oscillator
                                                    10
11
   ωc = 2πfc = 2π(f0 + KVCOV0)

                                  12
13
   Each harmonic at the control line of a VCO
    will generate an infinite number of spurs at
    multiple frequencies around the carrier
    frequency of the VCO

   The magnitude of a spur depends on the
    Bessel functions and depends on the KVCO

                                               14
Blocking of the fractional spurs




                                   15
16
17
Simulation results




                     18
19
20
VCO output spectrum of the conventional PLL   VCO output spectrum of the PLL
                 (zoomed)                          with DTF (zoomed).
                                                                               21
    Conclusion
   Fractional-N frequency synthesizers with
    low fractional spurs

   Discrete-time comb filter, switched
    capacitor techniques

   Simulation results

                                               22
    References
   Kratyuk, V.; Hanumolu, P.K.; Un-Ku Moon; Mayaram,
    K.;Circuits and Systems, 2005. ISCAS 2005. IEEE
    International Symposium on 23-26 May 2005
    Page(s):2807 - 2810 Vol. 3
    Digital Object Identifier 10.1109/ISCAS.2005.1465210

   Volodymyr Kratyuk, Pavan Kumar Hanumolu, Un-Ku
    Moon and Kartikeya Mayaram
   School of Electrical Engineering and Computer Science
    Oregon State University, Corvallis, Oregon 97331
                                                            23
   Thank You For Your Attention !




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