Meaning
Sensitivity of a quartz crystal resonator to mechanical forces defines how much its resonant frequency shifts when subjected to external strain, acceleration, or pressure. This characteristic, known as the stress-frequency coefficient quartz, dictates the performance of reference oscillators in high-vibration environments like vehicles or industrial factories. It is measured in units of frequency change per unit of applied force or acceleration.
Mechanical Strain
Forces acting on the crystal package translate directly to the quartz blank through the internal support structure, bending the crystal lattice and changing its stiffness. In components with a high stress-frequency coefficient quartz, even a slight warping of the circuit board during soldering can cause a permanent frequency offset. This shift forces system designers to use flexible mounting pads or specialized stress-relief slots in the printed circuit board layout.
These layout adjustments decouple the oscillator package from the expansion and contraction of the motherboard, preventing frequency drift when the device heats up.
Mounting Effect
The design of the mounting clips that hold the quartz blank inside its metal or ceramic package must absorb external shock and vibration. Resonators with an optimized stress-frequency coefficient quartz use specialized stress-free mounting geometries to isolate the quartz blank from package stress. This isolation reduces the vibration-induced phase noise, keeping the communication link stable even under heavy mechanical turbulence.
System Tolerance
High-frequency communication systems specify a maximum limit for oscillator phase noise under vibration to ensure stable signal tracking. Knowing the stress-frequency coefficient quartz of the chosen component allows engineers to calculate the phase jitter that will occur during operating conditions. Selecting a crystal with a low coefficient ensures that the receiver tracking loop does not lose lock during mechanical shocks.
