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A DLL-Based Multi-Clock Generator Having Fast-Relocking and Duty-Cycle Correction Scheme for Low Power and High Speed VLSIs  

Hwang Tae-Jin (Department of Electronic Engineering, Soongsil University)
Yeon Gyu-Sung (Department of Electronic Engineering, Soongsil University)
Jun Chi-Hoon (Department of Electronic Engineering, Soongsil University)
Wee Jae-Kyung (Department of Electronic Engineering, Soongsil University)
Publication Information
Journal of the Institute of Electronics Engineers of Korea SD / v.42, no.2, 2005 , pp. 23-30 More about this Journal
Abstract
This paper describes a DLL(delay locked loop)-based multi-clock generator having the lower active stand-by power as well as a fast relocking after re-activating the DLL. for low power and high speed VLSI chip. It enables a frequency multiplication using frequency multiplier scheme and produces output clocks with 50:50 duty-ratio regardless of the duty-ratio of system clock. Also, digital control scheme using DAC enables a fast relocking operation after exiting a standby-mode of the clock system which was obtained by storing analog locking information as digital codes in a register block. Also, for a clock multiplication, it has a feed-forward duty correction scheme using multiphase and phase mixing corrects a duty-error of system clock without requiring additional time. In this paper, the proposed DLL-based multi-clock generator can provides a synchronous clock to an external clock for I/O data communications and multiple clocks of slow and high speed operations for various IPs. The proposed DLL-based multi-clock generator was designed by the area of $1796{\mu}m\times654{\mu}m$ using $0.35-{\mu}m$ CMOS process and has $75MHz\~550MHz$ lock-range and maximum multiplication frequency of 800 MHz below 20psec static skew at 2.3v supply voltage.
Keywords
Delay loked loop (DLL); fast-relocking; frequency multiplication; duty-ratio;
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