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This paper presents the design of a process-variation tolerant Delay-Locked Loop (DLL) for use in multiphase clock generation. A transistor sizing methodology to reduce delay variations with threshold voltage (Vt) mismatch in the Voltage Controlled Delay Line (VCDL) is proposed. Additionally, a new digital calibration scheme is proposed to further reduce the delay variations. A DLL was fabricated in a 0.6μm CMOS process and measurement results indicate reduction in the maximum mismatch in the timing error among the delay blocks from 40.1ps (3.28°) to 13.44ps (1.09°).
Date of Conference: 12-15 Dec. 2010