1. 1 A Low Spur Fractional-N Frequency Synthesizer Architecture 指導教授 : 林志明 教授 學生 : 黃世一 Circuits and Systems, 2005. ISCAS 2005. IEEE International Symposium on 23-26 May 2005 Page(s):2807 - 2810 Vol. 3

2. 2 Outline Abstract Introduction Fractional spurs Blocking of the fractional spurs Simulation results Conclusions References

3. 3 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

4. 4 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

5. 5 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

6. 6 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

7. 7 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

8. 8 Fractional spurs Fractional-N frequency synthesizers generate spurs at the output of VCO

9. 9 ω s = 2πf s fs - frequency of a spur V i - amplitude of the i-th harmonic ϕ i - phase of the i-th harmonic

10. 10 ω 0 = 2πf 0 f 0 - frequency of the free running oscillator V A - amplitude of oscillation Φ(t) - phase of the oscillator

11. 11

12. 12 ω c = 2πf c = 2π(f 0 + K VCO V 0 )

13. 13

14. 14 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 K VCO

15. 15 Blocking of the fractional spurs

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18. 18 Simulation results

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20. 20

21. 21 VCO output spectrum of the conventional PLL (zoomed) VCO output spectrum of the PLL with DTF (zoomed).

22. 22 Conclusion Fractional-N frequency synthesizers with low fractional spurs Discrete-time comb filter, switched capacitor techniques Simulation results

23. 23 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

24. 24 Thank You For Your Attention !