Reference Clock Generation in Sampled Data Systems

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  • Author: Paul Nunn
This article exam-ines the character-istics and perfor-mance of a reference clock for a sampled-data system. Reference clocks with excellent perfor-mance are required in GSM and UMTS wireless base stations and in tele-com-system subsections such as routers, add-drop multiplexers, and aggregation boxes. The reference clock in those systems is generally derived from a crystal-based module such as an XO, TCXO, VCXO, or OCXO. In turn, those devices are usually chosen to obtain the required frequency stability, jitter and phase noise performance. Within the last four years these modules have come to offer much small-er dimensions, higher fundamental crystal frequencies, improved phase noise and reduced jitter—all with substantial price reductions.