Journal of electromagnetic engineering and science

The Korean Institute of Electromagnetic Engineering and Science (한국전자파학회)
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A Lock-Time Improvement for an X-Band Frequency Synthesizer Using an Active Fast-Lock Loop Filter

  • Heo, Yun-Seong (Department of Radio Science & Engineering, Chungnam National University) ;
  • Oh, Hyun-Seok (Department of Radio Science & Engineering, Chungnam National University) ;
  • Jeong, Hae-Chang (Department of Radio Science & Engineering, Chungnam National University) ;
  • Yeom, Kyung-Whan (Department of Radio Science & Engineering, Chungnam National University)
  • Received : 2011.02.11
  • Published : 2011.06.30
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Abstract

In phase-locked frequency synthesizers, a fast-lock technique is frequently employed to overcome the trade-off between a lock-time and a spurious response. The function of fast-lock in a conventional PLL (Phased Lock Loop) IC (Integrated Circuit) is limited by a factor of 16, which is usually implemented by a scaling of charge pumper, and consequently a lock time improvement of a factor of 4 is possible using the conventional PLL IC. In this paper, we propose a novel external active fast-lock loop filter. The proposed loop filter provides, conceptually, an unlimited scaling of charge pumper current, and can overcome conventional trade-off between lock-time and spur suppression. To demonstrate the validity of our proposed loop-filter, we fabricated an X-band frequency synthesizer using the proposed loop filter. The loop filter in the synthesizer is designed to have a loop bandwidth of 100 kHz in the fast-lock mode and a loop bandwidth of 5 kHz in the normal mode, which corresponds to a charge pumper current change ratio of 400. The X-band synthesizer shows successful performance of a lock-time of below 10 ${\mu}sec$ and reference spur suppression below -64 dBc.

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