Free-Running Ring Frequency Synthesizer

Abstract

A digital processor uses a single free-running ring oscillator to synthesize multiple clocks without analog circuits or feedback loops. Fabricated in 0.18mum technology, the 4mm2 die integrates 6 independent spread-spectrum synthesizers with <0.1ps period resolution. The synthesizers operate from 3 to 400MHz with a jitter <85ps, meeting PCIe clock-jitter requirements