Acceleration Sensitivity Characteristics of Quartz Crystal Oscillators

The resonant frequency of every quartz crystal is affected by acceleration forces. The nature of th effect depends on the type of force that is being applied. Changes in the static gravitational force being experienced such as tilting or rotation will cause a step offset in frequency. Time dependent acceleration or vibration will frequency modulate the output. A shock pulse will cause a sharp temporary perturbation in the output frequency.The magnitude of these frequency shifts is determined by the quartz crystal’s acceleration or “g-sensitivity” vector and the characteristics of the applied acceleration force. The range of typical g-sensitivities for bulk-mode quartz crystals can span several orders of magnitude, from less than 1x10-10 per g for a carefully made precision SC cut to greater than 1x10-7 per g for a low cost AT.

Since the magnitude of these effects is relatively small, they go undetected in many applications with standard oscillators such as VCXO’s and clocks.However with precision ovenized oscillators or those that undergo severe environmental conditions, the inherent acceleration sensitivity can be very significant. If the oscillator is deployed in a high vibration environment such as an airborne platform, increased phase noise can degrade the system performance more than all other sources of noise combined. But even in a benign environment, a high stability OCXO may experience significant frequency shifts. With knowledge of the operating environment that an oscillator will experience and an understanding of the acceleration sensitivity of the quartz crystal, it is possible to predict and plan for the expected frequency errors.

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