We usually need our customers to provide center frequency, cut type (AT/BT), model, resistance (ESR), frequency tolerance, frequency stability, load capacitance, operating temperature range, driving power, aging rate and other related parameters, etc.
Frequency stability is the maximum deviation between the allowable frequency and the reference frequency under the operating temperature range. The reference frequency usually refers to the frequency of the crystal oscillation at room temperature. Frequency stability is usually characterized by ppm.
The frequency tolerance of a crystal refers to the amount of offset that is allowed to exist in PPM with the standard frequency at a particular temperature.
The characteristics of crystals are largely determined by the crystal rods being cut into wafers in advance according to predetermined angles, and the most commonly used cutting methods are AT-cut.
Usually at the same frequency, the BT cut wafer is thicker than AT cut wafer, so the higher frequency wafer can be achieved by BT cutting.
How will the
crystal perform when the temperature is not in the specified range? The performance
of crystals will be affected when it is not in the specified temperature range.
We strongly recommend to avoid such situations. Otherwise it will cause the
frequency drift. Even worse, it may cause a total circuit failure.
Aging is the phenomenon of crystal frequency change due to the time. Aging causes the frequency to shift in two different directions.
Aging causes the overall drift of the wafer frequency of the oscillator's internal loading. Aging is caused by two factors, pollution and stress.
It is proved that the contamination on the crystal surface often leads to the negative frequency shift, whereas the excess pressure leads to the positive frequency deviation. When the wafer is placed on the bracket (pedestal), it will likely be placed on the structure, stretching or twisting. This will result in pressure on the wafer. Such pressure can be released with time, resulting in a positive frequency shift. When placing the wafer, the proper placement of the wafer and the use of the appropriate base will help to eliminate or reduce unwanted stress.
For finished products, the thermal cycle will help release the pressure. The surface contamination of the wafer exists in every aspect of production. The surface dirt on the wafer causes a large load to cause a negative shift in frequency.
Cleanness of all processes and improving the surface cleanness of the wafer will help minimize pollution. Crystals can, to some extent, be "pre-aging" to minimize the effects of aging. Because the aging characteristic curve is close to the logarithmic curve, the aging of the crystal usually appears in the first few years after the crystal is made. By contrast, in the first year, the crystal frequency changes more frequently and faster than the second year and later.
The instability of quartz crystals is a measure of the frequency change caused by the wafer load capacitance. The circuit designer can design a working frequency range by changing or modifying the crystal load capacitance. The operating frequency range is determined by the instability of the crystals under the specified (varying) load capacitance range.
The crystal has a frequency oscillation that is not related to its fundamental frequency or overtone. The unwanted frequencies are called parasitic frequencies. The parasitic frequency effect can be suppressed by changing the size of the wafer, the design of the electrode size and the amount of silver in the crystal fabrication and production process.
