What is the most accurate crystal oscillators? | Xtalong
Crystal oscillator (xtal) is a precision frequency component that can provide stable and accurate frequency signals. However, due to the different slicing process, compensation method and circuit structure, the frequency characteristics of crystal oscillators are also different. Three important parameters must be considered when selecting models: frequency accuracy, frequency stability and long-term stability.
1. Frequency tolerance
Frequency Tolerance is to adjust the frequency difference, which is the deviation between the output frequency fx of the crystal oscillator at room temperature (+25°C) and the center nominal frequency f0.
This parameter is greatly affected by the wafer material and environment, and generally ranges from a few ppb to ±100ppm. The frequency accuracy of common crystal oscillators is as follows:
xtal crystal resonator: 50ppm
Thermistor xtal: ±10ppm
VCXO voltage-controlled crystal oscillator: ±20ppm
TCXO temperature-compensated crystal oscillator: about ±0.2ppm
OCXO constant temperature crystal oscillator: several ppb
For example, the 25°C frequency accuracy of T2520 thermal crystal oscillator (xtal) of Taijing Technology and the frequency stability in the operating temperature range of -30°C ~ +85°C both reach ±10ppm, which has reached the crystal oscillator (XO ) accuracy, and higher precision products can also be customized according to user needs.
In practical applications, the accuracy of the crystal oscillator may be affected by ±1ppm of voltage changes, ±5ppm of soldering temperature changes, ±3PPM of mechanical vibration and shock, and 10~20ppm or more of stray capacitance. Temperature has an effect of 5~20ppm. Therefore, a margin of 10ppm should be reserved when selecting a model. If a frequency accuracy of ±30ppm is required, a crystal oscillator with a frequency accuracy of ±20PPM is generally selected.
2. frequency stability
The frequency stability of the crystal oscillator (Frequency Stability) usually refers to the temperature stability, that is, the temperature frequency difference, which is a short-term stability indicator that measures the output frequency of the crystal oscillator that may change due to temperature changes during operation. Timing errors may occur if the frequency drifts beyond the application's expectations.
Among all crystal oscillators, the frequency stability of OCXO constant temperature crystal oscillator is the highest, which can reach the ppb level (10-9), the stability of TCXO temperature compensated crystal oscillator is below 1ppm, and the stability of ordinary crystal oscillator is within 100ppm. The stability of atomic clocks is higher, generally above 10-11.
For communication applications such as smartphones, GPS modules, WIBRO, DMB, and transponders, stability below ±1ppm is generally required, which requires the use of TCXO temperature-compensated crystal oscillators.
3. Frequency Aging
The long-term stability (Frequency Aging) refers to the annual aging rate, which is generally ±3ppm/year (the first year, at room temperature of 25°C), and it will tend to be stable in the future.
After a long period of slow aging of the crystal oscillator, the output frequency will slowly drift. Since the datasheets of most crystal oscillator manufacturers only provide one-year aging data at 25°C, for industrial applications, users can ask suppliers for 10-year aging data at higher temperatures, because crystal oscillator parameters can be customized.