A 2 . 5 V CMOS Delay-Locked Loop for an 18 Mbit , 500 Megabytek DRAM

This paper describes clock recovery circuits specifically designed for the hostile noise environment found aboard dynamic RAM chips. Instead of a phase-locked loop having a voltage-controlled oscillator, these circuits implement a delaylocked loop, thereby achieving low jitter and reduced sensitivity to noise on the substrate and the power supply rails. Differential signals are employed both in signal paths and in control paths, further decreasing noise sensitivity and simultaneously allowing operation from low voltage supplies. An unorthodox voltagecontrolled phase shifter, operating on the principle of quadrature mixing, yields a circuit with unlimited delay range (modulo 2s radians). Minor loops, enclosed within the overall loop feedback path, perform active duty cycle correction. Measured results show peak-to-peak jitter of 140 ps on the internal clock signal, and 250 ps on the external data pins, sufficiently small to allow 500 Megabytels transfer rates at the YO interface.