Chipsun Knowledge Collection | Determining Factors of Crystal Oscillator Frequency
Dear readers, most crystal oscillators are composed of quartz or ceramic materials combined with internal wafers, and the frequency of a crystal oscillator depends on the thickness of the wafer.
Firstly, in terms of manufacturing processes, the size and thickness of the wafer are closely related to the frequency of the crystal oscillator. Generally, the higher the frequency of a quartz crystal oscillator, the thinner the required quartz wafer.
The determining factors of crystal oscillator frequency mainly include the following aspects:
01 Wafer physical parameters
Size and thickness: The frequency is inversely proportional to the wafer thickness. The higher the frequency, the thinner the wafer (such as only the thickness of a hair). The length and width dimensions also affect the equivalent vibration characteristics.
Cutting method: Different angle cuttings such as AT cut and BT cut will affect the frequency stability. For example, F cut is suitable for environments with large temperature changes.
02 Influence of external conditions
Temperature: Temperature changes can cause frequency drift, so it is necessary to select crystal oscillators with different temperature ranges such as industrial grade and automotive grade according to the application scenario.
Load capacitance/voltage: Passive crystal oscillators need to match the load capacitance, and active crystal oscillators need to determine the working voltage.
03 Other factors
Package size: There is a correlation between frequency and package size (such as common packages like 3225 and 2016).
Frequency tolerance: The frequency deviation (ppm value) at room temperature is also a key parameter.
Before ending today’s topic, let’s learn about the differences in usage between fundamental frequency crystal oscillators and overtone crystal oscillators. Firstly, there must be differences in their usage. For example, a fundamental frequency crystal can work as long as it is connected to an appropriate capacitor, while an overtone crystal oscillator needs the cooperation of an inductor and a capacitor to oscillate at the overtone frequency; otherwise, it can only oscillate at the fundamental frequency.