Copyright © 2008 The Institute of Electronics, Information and Communication Engineers
Special Section on Analog Circuit Techniques and Related Topics -- Papers |
A 3.2-GHz Down-Spread Spectrum Clock Generator Using a Nested Fractional Topology
1 The author is with the Department of Electrical Engineering, National Chung Hsing University, Taichung, Taiwan, R.O.C. E-mail: ycy{at}dragon.nchu.edu.tw, 2 The author is with the Graduate Institute of Electrical Engineering, National Chung Hsing University, Taichung, Taiwan, R.O.C., 3 The author is with the Sonix Technology Corp., Hsinchu, Taiwan, R.O.C.
A high-speed triangular-modulated spread-spectrum clock generator using a fractional phase-locked loop is presented. The fractional division is implemented by a nested fractional topology, which is constructed from a dual-modulus divide-by-(N–1/16)/N divider to divide the VCO outputs as a first division period and a fractional control circuit to establish a second division period to cause the overall fractional division. The dual-modulus divider introduces a delay-locked-loop network to achieve phase compensation. Operating at the frequency of 3.2 GHz, the measured peak power reduction is around 16 dB for a deviation of 0.37% and a frequency modulation of 33 kHz. The circuit occupies 1.4 x 1.4 mm2 in a 0.18-µm CMOS process and consumes 52 mW.
Key Words: spread spectrum clock generation, fractional phase-locked loop, delay-locked loop, phase compensation, fractional divider
Manuscript received June 14, 2007. Manuscript revised September 2, 2007.
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