What are the Factors that Affect the Frequency Stability of Crystal Oscillator？

"Frequency Stability" is used to define the ability of an oscillator to maintain a single fixed frequency for as long as possible within a time interval. Specifically, Frequency Stability of oscillator is generally defined as the permissible deviation from the rated temperature range (Typically -40° ~ +85°C). It is important to note that when selecting an oscillator, the "frequency deviation" and "frequency stability" are cumulative and are usually expressed in parts per million (PPM).

It should be note that even though the electronic crystals’s factory set to the initial frequency (the electrical parameter stated in the specification), in practice it cannot always be kept absolutely constant. Objectively speaking, the frequency stability of the crystal is always in a state of flux, with variations either showing regularity or sometimes irregularity.

In the circuit application of electronic crystals, frequency deviations are caused by variations in the circuit's characteristic values (circuit components, crystal electrical parameters, supply voltage, stray capacitance, output load, etc.). Each component of the oscillation circuit has the potential to affect the stability and accuracy of the actual output frequency of the electronic crystals.

Other factors affecting the frequency deviation of the electronic crystals are as follows：

The quality of the electronic crystals 

As a core electronic component that provides frequency, when selecting or purchasing electronic crystalss, please select qualified electronic crystals products in strict accordance with the chip specified electronic crystals parameters. The crystal is not qualified, such as DLD2 is not up to standard, air tightness is not qualified and other factors will directly lead to crystal frequency instability under high and low temperature changes.

Related electronic components

If other electronic components in the circuit are not in their rated operating range, some parameters of the electronic crystals may be affected, thus affecting its frequency stability. Therefore, components such as resistors R, inductors L, capacitors C and other components need to be of the correct quality and used correctly to ensure the stability of the electronic crystals’s peripheral circuitry.

Mechanical vibration

Mechanical vibration can bring hidden problems to the normal operation of the electronic crystals. It is recommended to avoid interference by isolating the electronic crystals circuit from the source of mechanical vibration.

Power supply voltage

One of the factors contributing to frequency deviation is the variation of the power supply (the operating voltage applied to the active device), however this problem can be overcome by using a regulated power supply. Due to the transformer, any variation in the load coupled to the oscillation circuit may result in a change in the effective resistance in the circuit, resulting in a drift in frequency.

Temperature variations in the circuit board

When the circuit is operated for a long time, heat starts to build up. The results show that the electrical parameters of components such as resistor R, inductor L and capacitor C change with temperature, causing the electronic crystals frequency stability to be affected. The resistor R, inductor L and capacitor C change slowly and the electronic crystals frequency will change slowly.