Fractional-N Frequency Synthesis: Overview and Practical Aspects with FIR-Embedded Design

  • Rhee, Woogeun (Institute of Microelectronics, Tsinghua University) ;
  • Xu, Ni (Institute of Microelectronics, Tsinghua University) ;
  • Zhou, Bo (Institute of Microelectronics, Tsinghua University, Beijing, China and now with Beijing Institute of Technology) ;
  • Wang, Zhihua (Institute of Microelectronics, Tsinghua University)
  • Received : 2012.09.05
  • Accepted : 2012.12.06
  • Published : 2013.04.30


This paper gives an overview of fractional-N phase-locked loops (PLLs) with practical design perspectives focusing on a ${\Delta}{\Sigma}$ modulation technique and a finite-impulse response (FIR) filtering method. Spur generation and nonlinearity issues in the ${\Delta}{\Sigma}$ fractional-N PLLs are discussed with simulation and hardware results. High-order ${\Delta}{\Sigma}$ modulation with FIR-embedded filtering is considered for low noise frequency generation. Also, various architectures of finite-modulo fractional-N PLLs are reviewed for alternative low cost design, and the FIR filtering technique is shown to be useful for spur reduction in the finite-modulo fractional-N PLL design.


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