OCXO G-Sensitivity: Understanding Acceleration Sensitivity

This page describes OCXO G-sensitivity, covering the definition, formula/equation, and units of measurement associated with OCXOs.

OCXO G-sensitivity Definition

OCXO stands for Oven Controlled Crystal Oscillator. G-sensitivity refers to the change in the output frequency of an oscillator when subjected to an acceleration force. It’s also known as Acceleration Sensitivity.

This phenomenon arises because the quartz crystal used in OCXOs is an electro-mechanical device. Applying voltage across the crystal causes it to oscillate, and conversely, applying vibration induces a voltage.

Different types of OCXOs exist, including those using AT-cut, IT-cut, and SC-cut crystals. SC-cut crystals exhibit lower g-sensitivity due to their stress compensation feature.

OCXO g-sensitivity is typically measured in units of ppb/g (parts per billion per g). Figure 1 (not included here, but see the link below) illustrates the internal components of an OCXO.

The g-sensitivity for bulk mode quartz crystals can range from less than 1x10^-10 per g for meticulously crafted SC-cut crystals to greater than 1x10^-7 per g for lower-cost AT-cut crystals.

OCXO G-sensitivity Formula or Equation

The following equations or formulas are used for OCXO G-sensitivity.

The induced phase noise degradation of an oscillator can be calculated from its g-sensitivity.

By knowing the Power Spectral Density (PSD) of the vibration input, it’s possible to compute the g-sensitivity of the crystal from the resultant phase noise plot.