A Wideband Clock Generator Design using Improved Automatic Frequency Calibration Circuit

개선된 자동 주파수 보정회로를 이용한 광대역 클록 발생기 설계

  • Received : 2010.12.31
  • Accepted : 2011.01.26
  • Published : 2011.02.01


In this paper, a wideband clock generator using novel Automatic frequency calibration(AFC) scheme is proposed. Wideband clock generator using AFC has the advantage of small VCO gain and wide frequency band. The conventional AFC compares whether the feedback frequency is faster or slower then the reference frequency. However, the proposed AFC can detect frequency difference between reference frequency with feedback frequency. So it can be reduced an operation time than conventional methods AFC. Conventional AFC goes to the initial code if the frequency step changed. This AFC, on the other hand, can a prior state code so it can approach a fast operation. In simulation results, the proposed clock generator is designed for DisplayPort using the CMOS ring-VCO. The VCO tuning range is 350MHz, and a VCO frequency is 270MHz. The lock time of clock generator is less then 3us at input reference frequency, 67.5MHz. The phase noise is -109dBC/Hz at 1MHz offset from the center frequency. and power consumption is 10.1mW at 1.8V supply and layout area is $0.384mm^2$.


  1. Won-Young Lee, Lee-Sup Kim, "A spread spectrum clock generator with spread ratio error reduction scheme for DisplayPort main link" Circuits and Systems, 2009. ISCAS 2009. IEEE International Symposium on, pp.185-188, May 2009.
  2. VESA DisplayPort Standard Version 1.1 March 19, 2007
  3. William B. Wilson, Un-Ku Moon, Kadaba R. Lakshmikumar, Ling Dai, "A CMOS self-calibrating frequency synthesizer," IEEE J. Solid-State Circuits, vol. 35, no. 10, pp. 1437-1444, Oct 2000.
  4. 김성근, 김영신, 김상우, 조후현, 부영건, 이강윤, "DisplayPort용 TxPLL과 Spread Spectrum clock Generator의 설계," 대한전자공학회 학술대회, 380-382쪽, 2009년
  5. Han-il Lee, Je-Kwang Cho, Kun-Seok Lee, In-Chul Hwang, Tae-Won Ahn, Kyung-Suc Nah, Byeong-Ha Park, "A $\Sigma-\Delta$ fractional-N frequency synthesizer using a wide-band integrated VCO and a fast AFC technique for GSM/GPRS/WCDMA applications," Solid-State Circuits, IEEE Journal of, Vol 39, no. 7, pp. 1164-1169, 2004.
  6. Kun-Seok Lee, Eun-Yung Sung, In-Chul Hwang , Byeong-Ha Park, "Fast AFC technique using a code estimation and binary search algorithm for wideband frequency synthesis," Solid-State Circuits Conference, 2005. ESSCIRC 2005. pp. 181, sept 2005.