It’s about time for 5G – and about giving radios precise local clock sources even in harsh environments: Page 3 of 6

July 04, 2019 //By Markus Lutz, CTO and Founder, SiTime Corporation
It’s about time for 5G – and about giving radios precise local clock sources even in harsh environments
Redefining best practices for implementing 5G timing and synchronization solutions

Shock and vibration can be particularly problematic. Vibration can cause quartz oscillators to easily go out of specification, potentially for as long as the vibration continues. This span of time can be minutes for a passing freight train or even longer if, for instance, the oscillator is subjected to steady gusts on a windy day. Temperature also presents challenges. Depending on the season of the year and where the oscillator is deployed, it can be exposed to extremely hot or cold conditions that can last for prolonged periods of time.

Also challenging are rapid temperature shifts, such as when a black box in the sun cools quickly as a rain cloud passes by, or in areas where colliding weather fronts and a moving jet stream bring together hot and cold air masses that can whipsaw ambient temperature from one extreme to another in a matter of minutes. Quartz oscillators have difficulty dealing with these effects, which can lead to frequency changes of hundreds of parts per billion (ppb). In many cases it may take several minutes for the quartz oscillators to return to the specified frequency due to the slow oven-control time constants. 

None of this is satisfactory in the 5G environment, where the latency budget of the network behind the radios is now 5 to 10 ns, and the maximum time difference between radios is limited to 130 ns. To solve these problems, MEMS timing solutions use a combination of programmable analog, innovative packaging and high-performance temperature-compensation algorithms that deliver 20 times better timing precision than is possible with quartz-based alternatives. The ability of these MEMS OCXOs to maintain sub-ppb frequency stability under challenging environmental stressors will have a transformative impact on 5G system deployment. The technology also gives developers an opportunity to substantially re-think their design strategies so they can take full advantage of the new capabilities that MEMS OCXOs deliver. 

Figure 2: Comparison of measured frequency stability over temperature (hysteresis) of SiTime MEMS Stratum-3E OCXO and three quartz Stratum-3E OCXOs.

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