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As an "insider" in the crystal oscillator industry or a newbie who has just entered the crystal oscillator industry, it is particularly necessary to understand the professional terms of crystal oscillators. Today, Xiao Yang will sort out some basic crystal oscillator professional terms for everyone:
1. Nominal frequency
The nominal frequency refers to the frequency of vibration of the quartz crystal in the crystal oscillator under a normally matched oscillation circuit, expressed in MHz or KHz.
For example: the quartz crystal vibrates one million times in 1 second, then the frequency is 1MHz.
2. Adjustment frequency difference
Refers to the maximum allowable deviation between the actual output frequency and the nominal frequency of the crystal oscillator at room temperature (25℃). The frequency error range of the crystal oscillator at standard temperature. This error is usually expressed in ppm (parts per million).
For example: for a crystal oscillator with a nominal frequency of 10MHz, if the adjustment frequency difference is ±10ppm, the actual frequency may fluctuate between 9.9999MHz and 10.0001MHz. The smaller the adjustment frequency difference, the higher the frequency accuracy of the crystal oscillator.
3. Temperature frequency difference
Refers to the maximum allowable deviation between the actual output frequency and the nominal frequency of the crystal oscillator within the operating temperature range.
When the crystal oscillator works at different temperatures, the frequency may fluctuate to a certain extent due to temperature changes. This deviation is usually also expressed in ppm (parts per million).
For example: the temperature frequency difference of the crystal oscillator is ±20ppm. Within the specified temperature range, the actual frequency may be up to 20ppm higher or lower than the nominal frequency. The smaller the temperature frequency difference, the better the frequency stability of the crystal oscillator, and the less affected by temperature changes.
4. Operating temperature range
The operating temperature range is the temperature range in which the crystal oscillator can work normally. Within this range, the frequency deviation and other performance of the crystal oscillator can remain normal.
For example, the operating temperature range of the crystal oscillator is -40℃ to 85℃, and it can operate stably within this range. Beyond this range, the performance may not be good. The wider the operating temperature range, the more adaptable the crystal oscillator is to different environments.
5. Storage temperature range
Refers to the temperature range in which the crystal can be safely stored when it is not working (not powered). The storage temperature range of a crystal is -55℃ to 125℃. As long as it is placed in this range, its performance will not be bad. But if it exceeds this range, it may be used for a few years less or its performance may deteriorate. The storage temperature range is generally wider than the operating temperature range to make the crystal safer during transportation or storage.
6. Load capacitance (load capacitance is determined by external capacitance and stray capacitance in the circuit)
① Load capacitance refers to the external capacitance connected in series with the crystal, which directly affects the resonant frequency of the crystal. The load capacitance is like a "frequency modulator" for the crystal-when the load capacitance changes, the output frequency of the crystal will also change.
② Common load capacitance values are: 8pF, 9pF, 10pF, 12pF, 12.5pF, 15pF, 18pF, 20pF, etc. Different load capacitance values are suitable for different circuit design requirements.
③ The calculation formula of load capacitance is: CL = (Cg × Cd) / (Cg + Cd) + Cs.
· Cg and Cd are the external capacitance values connected to the two pins of the crystal oscillator.
· Cs is the stray capacitance in the circuit, usually 3pF to 5pF.
7. Static capacitance
Refers to the capacitance formed between the quartz chip and the two electrodes inside the crystal oscillator. A small part of the capacitance comes from the conductive material between the quartz chip and the connecting wire, as well as the capacitance of the crystal oscillator package shell.
8. Cutting method
Depending on the requirements of different application scenarios and working temperatures, quartz crystals will be cut at specific angles to form different cutting methods. Cutting types include: AT cutting, BT cutting, CT cutting, SC cutting, DT cutting, NT cutting, GT cutting, etc. The different angles of each cutting method will affect the elastic constant, piezoelectric constant and dielectric constant of the crystal, and thus affect its frequency characteristics and temperature stability.
The cutting angle determines the vibration mode and temperature-frequency characteristics of the crystal oscillator. Quartz crystals have a crystal axis, and when cutting, they are cut at a specific angle perpendicular to the crystal axis.
9. Vibration mode
Due to the electric field effects of different quartz cutting angles and different electrode shapes, quartz chips exhibit various vibration modes. The most frequently generated vibration modes can be divided into bending mode, stretching mode, surface shear mode and thickness shear vibration mode.
