SC-cut and AT-cut crystals are widely used in oscillator applications, but they offer distinct differences in terms of frequency stability. SC-cut crystals are known for their superior performance in high-precision applications, while AT-cut crystals are more common in general-purpose devices. Let’s explore how the frequency stability of these two crystal cuts compares.
Frequency Stability: The Key Differences
SC-Cut Crystals:
• Exceptional Stability: SC-cut crystals exhibit frequency stability of less than ±10 ppb (parts per billion) across a wide temperature range.
• Stress Compensation: The stress-compensated design minimizes sensitivity to mechanical and thermal stresses, contributing to consistent frequency stability.
• Higher Turning Point Temperature: The turning point for SC-cut crystals is around +90°C, allowing better performance at elevated temperatures.
• Low Aging Rates: Aging rates are typically ~0.1 ppm per year, providing long-term stability in critical applications.
AT-Cut Crystals:
• Good Stability: AT-cut crystals provide frequency stability in the range of ±15 ppm across -40°C to +85°C.
• Higher Thermal Sensitivity: More prone to frequency variations due to temperature changes, especially in extreme conditions.
• Lower Turning Point: The turning point is around +27°C, making AT-cut crystals less suitable for high-temperature applications.
• Higher Aging Rates: Aging rates are approximately 1 ppm per year, which is less favorable for long-term precision.
Thermal and Stress Sensitivity
• SC-Cut Crystals:
• Designed to resist thermal and mechanical stresses, resulting in minimal frequency shifts.
• Reduced sensitivity makes them ideal for dynamic and extreme environments.
• AT-Cut Crystals:
• More sensitive to stress and temperature fluctuations.
• Better suited for stable environments with limited stress and temperature variation.
Applications
SC-Cut Crystals:
• Used in Oven Controlled Crystal Oscillators (OCXOs) for high-precision applications:
• Telecommunications (e.g., 5G networks)
• Aerospace and defense systems
• Scientific instrumentation
AT-Cut Crystals:
• Commonly found in general-purpose oscillators:
• Consumer electronics
• Basic timing devices
• Industrial equipment
Trade-Offs
• SC-Cut Crystals:
• Higher cost due to complex manufacturing and tight tolerances.
• Larger size in some applications.
• AT-Cut Crystals:
• More cost-effective and widely available.
• Trade-offs in stability and aging performance.
Conclusion
When it comes to frequency stability, SC-cut crystals significantly outperform AT-cut crystals, making them the preferred choice for applications requiring exceptional precision and long-term reliability. However, the selection between SC-cut and AT-cut crystals ultimately depends on the specific requirements of the application, balancing performance with cost and environmental considerations.
DEI recommend P/N:
OCXO1615CV-LP
OCXO1615CVD-LP
OCXO3627CR-ULG
OCXO2114BM-LP-16.384MHz-A-V
OCXO2525CVH-LP-100MHz-A-V