All-Digital Delay-Locked Loop/Pulsewidth-Control Loop With Adjustable Duty Cycles

Abstract

An all-digital delay-locked loop (DLL) and an all-digital pulsewidth-control loop (PWCL) with adjustable duty cycles are presented. For the DLL, by using the flash time-to-digital conversion, both the phase alignment and the duty cycle of the output clock are assured in 10 cycles. For the PWCL, the sequential time-to-digital conversion is adopted to reduce the required D-flip-flops and lock within 28 cycles. For both of the proposed circuits, the requirement of the input clock with 50% duty cycle is eliminated. The proposed circuits have been fabricated in a 0.35-/spl mu/m CMOS process. The proposed DLL generates the output clock with the duty cycle of 25%, 50% and 75%, and the operation frequency range is from 140 to 260 MHz. For the proposed PWCL, the duty cycle is adjusted from 30% to 70% in steps of 10%. The operation frequency range is from 400 to 600 MHz.