It’s about time for 5G – and about giving radios precise local clock sources even in harsh environments: Page 4 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

New 5G best practices with MEMS oscillators

MEMS oscillators create a new set of best practices for deploying accurate network timing sources.  First, they eliminate the need for developers to restrict their OCXO printed circuit board (PCB) placement options. The sensitivity of quartz OCXOs to environmental stressors has required that they be separated from any sources of heat and airflow-induced thermal shock. These board placement constraints have complicated routing and created potential signal integrity problems. While developers have tried to solve this problem by using specialized plastic OCXO covers for thermal and airflow isolation, this introduces additional manufacturing steps and production complexity. 

These concerns do not exist with MEMS OCXOs, which have 20 times the vibration immunity of quartz. MEMS OCXOs have much better dynamic stability with frequency slope versus temperature (ΔF/ΔT) of ±50 ppt/°C typical (ppt = parts per trillion) and an Allan deviation (ADEV) of 2e-11 under airflow (see Figures 3A and 3B). MEMS OCXOs eliminate the need to worry about protective components or mechanical shielding during board design, and on-chip regulators mean there is no need for external LDOs or ferrite beads. Additionally, MEMS oscillators are resistant to microphonic and/or board bending effects, which is a key consideration for large telecom PCBs. Without these placement constraints, designers will have significantly greater freedom to place the components based on other criteria such as less cross coupling, reduced EMI, and higher density to save space. 

Figure 3A: Comparison of measured frequency slope versus temperature (ΔF/ΔT) of SiTime MEMS Stratum-3E OCXO and three quartz Stratum-3E OCXOs.

Figure 3B: MEMS Stratum-3E OCXO showing an Allan deviation (ADEV) of 2e-11 under airflow.

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