OCXOs are used as local reference clocks in telecommunication systems. Quartz-based oscillators provide best spectral purity because of its high Quality (Q) factor. Temperature stability and ageing performance of OCXOs enable them to be adequate enough for most of the equipment, node and station clocks.

OCXO technology has gone through significant advancements in recent years. The performance level that can be achieved by a specific size and power level has improved by one or more order of magnitude in the recent years. This paper discusses the recent evolution's in the OCXO technology. Improved, smaller sized crystals, very low g sensitive crystal design techniques, optimized heater, and sensor techniques, integrated electronic functions, in-built temperature post-compensation engines and real-time on-board ageing compensation techniques result in performances closer to the hysteresis limit of the crystals. Today, a given size of the OCXO improves the performance by one to two orders of magnitude compared to a conventional style OCXO.