Known as "pullability," this characteristic of quartz crystals, however, is limited – if you exceed the tolerance sensitivity, steady oscillation is no longer assured.
Specific alterations in the load capacitance makes it possible to change the frequencies of the quartz crystals slightly, optimising them for particularly high frequency-precision requirements. Manufacturers trim quartz crystals so that they operate within the promised range across the specified range of the load capacitance. Load capacitance: The right load capacitance (CL) of the oscillator circuit (= capacitance C, which the quartz oscillator recognises at its connections) is crucial when it comes to maintaining the frequency as precisely as possible.Tip: For particularly high demands on frequency stability, it makes sense to look at using temperature-compensated crystal oscillators. Developers can therefore take temperature influences into account in advance and compensate if necessary. Frequency stability across operating temperature range: Manufacturers specify both frequency stability across the operating temperature range and frequency deviation in ppm per K change in temperature.By choosing a suitable frequency tolerance, the best possible solution in terms of economical operation and functional security can be achieved for the demands of the particular application. Frequency tolerance at 25☌: By specifying the frequency tolerance (= maximum expected total deviation from the rated frequency at an ambient air temperature of +25☌ and operation within the permitted parameters), the manufacturer guarantees that the oscillating frequency of the quartz crystal will stay within the permissible range.However, this prevents the application from staying with the guaranteed tolerances. Therefore, by cutting at the correct angle, the difference does not affect the characteristics of a crystal oscillator. If the limit values of the datasheet are overstepped, this does mean that problems necessarily occur immediately, and, depending on the circumstances, operation can continue. Operating temperature range: Quartzs demonstrate a certain level of temperature dependency.Thus, an 8MHz quartz crystal measures around 7x5mm while a 20MHz quartz crystal just 2x1.6mm – crucial for circuit design. Quartz crystals with higher frequencies are usually available in smaller mounting forms. Frequency: The frequency of common quartz crystals lies between 32.768kHz and approx.not every quartz crystal is available in every mounting form. Note: For technical reasons, a quartz oscillator cannot be reduced in size arbitrarily i.e. Quartz crystals in SMD packages offer considerably more compact constructions, measuring for example just 1.6x1.2x0.3mm. With this type, the packages are typically over 6mm long, and are therefore not suitable for space-saving applications. Package form: A hermetically sealed and radially wound metal package is generally used with quartz crystals for conventional mounting (THT), including for clock crystals with a frequency of 32.768MHz.
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