Chipsun Knowledge Collection | Translation of Crystal Oscillator-Related Content
As a core component of electronic devices, the frequency stability of a crystal oscillator directly affects system performance. Temperature changes alter the physical properties of the quartz crystal inside the oscillator, leading to drift in its resonant frequency — a phenomenon known as the frequency-temperature effect. Different quartz crystal cutting angles result in significant variations in temperature coefficients. Among them, AT-cut crystal oscillators exhibit excellent performance over a wide temperature range, making them the first choice for most electronic devices.
1. Relationship Between Crystal Oscillator Frequency and Temperature
1.1 Negative Correlation
There is a negative correlation between the frequency of a crystal oscillator and temperature: as temperature rises, the frequency decreases gradually; conversely, a drop in temperature causes the frequency to increase.For example, with the most common AT-cut quartz crystal, the frequency deviation curve versus temperature shows that the temperature-induced frequency deviation is 0 at 25°C. When the ambient temperature is above 25°C, the oscillator’s frequency deviation first decreases and then increases; when the temperature is below 25°C, the frequency deviation first increases and then decreases.
1.2 Temperature Characteristics
The cutting type of the quartz wafer directly affects the frequency variation curve. Different cutting types have distinct temperature characteristics, which cause the frequency to change with temperature. Specifically, quartz wafers undergo thermal expansion at high temperatures, resulting in frequency changes of the crystal oscillator.
2. Temperature Compensation Technologies
Temperature compensation technologies are mainly categorized into analog compensation and digital compensation:
- Digital compensation solutions: Utilize temperature sensors to collect environmental data, then perform frequency calibration by searching pre-stored compensation tables or conducting real-time calculations. The compensation accuracy can reach ±0.1ppm.
- Analog compensation: Adjusts the load capacitance through a thermistor network. A classic solution involves connecting a thermistor in parallel with a fixed capacitor, achieving a compensation accuracy of ±1.5ppm.
A specific model of GPS module adopts a third-order temperature compensation algorithm, achieving a frequency stability of ±0.05ppm within the temperature range of -55°C to +105°C.
3. Countermeasures Against Temperature Effects on Crystal Oscillators
- Select wide-temperature crystal oscillators: These oscillators cover a broad temperature range and can maintain frequency stability across it.
- Choose temperature-compensated crystal oscillators (TCXOs): Equipped with temperature compensation circuits, TCXOs automatically adjust their frequency to adapt to temperature changes, thereby maintaining frequency stability. The compensation circuit monitors temperature variations and adjusts the oscillator’s frequency, effectively mitigating and correcting frequency drift caused by temperature.
- Improve crystal oscillator manufacturing processes: Enhance the frequency-temperature stability of oscillators by optimizing material selection and processing techniques.
- Optimize crystal oscillator package design: Reduce uneven temperature distribution inside the oscillator by improving the thermal conductivity of the package, thus enhancing frequency stability.
- Design a rational heat dissipation system for electronic devices: Control the operating temperature of electronic devices within a specific range to minimize the impact of temperature on the oscillator’s frequency.