Is the crystal oscillator you chose "stable" enough?
Frequency difference | Temperature drift | Aging | Phase noise | Jitter
Five major indicators evaluate whether the crystal oscillator is stable!
The crystal oscillator is the benchmark for the timing of the electronic system. Once it is unstable, it is easy to cause communication packet loss, data errors, timing confusion, and even the whole machine crash, bringing serious consequences.
So, the question is:
· How to judge whether a crystal oscillator is stable enough?
· Which parameters in the data sheet are key?
Today, Xiao Yang will teach you a set of:
"Crystal oscillator stable word secrets"
Disassemble the five key indicators in the data sheet,
Help you make scientific selections and ensure stable system operation,
Engineers can also reap "stable happiness"~
01 Frequency tolerance
Keywords: Is it accurate when leaving the factory?
Frequency tolerance, also called initial frequency accuracy, is the deviation between the frequency of the crystal oscillator and the nominal value when it leaves the factory.
This is one of the key indicators in the data sheet, usually marked as Frequency Tolerance, which can be said to be the first step in judging whether the crystal oscillator is "stable or not".
Figure: YXC Data Sheet - Frequency Tolerance (Yellow Highlight)
＞ Indicator Definition
· Definition: The maximum deviation between the actual output frequency of the crystal oscillator and the nominal frequency under standard test conditions (usually 25℃, rated voltage, standard load).
· Unit: ±PPM (parts per million). The smaller the value, the more accurate the crystal oscillator is when it leaves the factory, and the faster the system frequency is.
＞ Selection Recommendations
· Whether the system can "accurately align the frequency" when it is first powered on depends to a large extent on the factory frequency accuracy of the crystal oscillator.
· For applications such as communication modules and electric meters that need to run stably as soon as they are turned on, this parameter should be paid special attention to.
02 Frequency Temperature Stability
Keywords: Is it stable under cold and hot changes?
Frequency temperature stability, also known as temperature frequency difference, is often expressed in data sheets as "Frequency v.s. Temperature".
It reflects the ability of the crystal to resist frequency drift caused by temperature changes, and is the key to evaluating whether it can operate stably in a wide temperature environment.
Figure: YXC Data Sheet - Frequency Temperature Stability (Yellow Highlight)
＞ Index Definition
· Definition: The maximum deviation of the output frequency relative to the nominal frequency of 25℃ within the entire operating temperature range.
· Unit: Usually expressed in ±PPM. In addition, constant temperature crystal oscillators are also often expressed in ±PPB, 1PPM=1000PPB.
＞ Selection Recommendations
· Standard crystal oscillator:
① Temperature deviation: ±10ppm ~ ±30ppm
② Application: Suitable for indoor environments with normal temperature or small temperature differences, suitable for consumer electronics, general industrial control and other fields, can balance frequency stability and cost, and meet most basic needs.
· Temperature Compensated Crystal Oscillator (TCXO):
① Temperature deviation: ±0.1ppm ~ ±2.5ppm
② Application: Built-in temperature compensation circuit, strong resistance to temperature drift. Suitable for environments with large temperature differences such as outdoor and vehicle-mounted, it is a common choice in the fields of positioning and communication.
· Oven-controlled crystal oscillator (OCXO):
① Temperature deviation: ±0.01ppb ~ ±500ppb
② Application: Built-in constant temperature system, minimal temperature drift. Dedicated to scenarios such as Beidou timing, 5G base stations, and precision instruments that pursue extreme frequency accuracy.
03 Aging rate
Keywords: Will it "drift" after long-term use?
Crystal oscillators will also "age" after long-term operation.
Aging rate is a key indicator to measure the frequency drift trend of crystal oscillators in long-term operation. The data sheet is usually marked as Aging, which affects the long-term stability of the system.
Figure: YXC data sheet-aging rate (yellow highlight)
＞ Indicator definition
· Definition: After long-term continuous operation, the crystal oscillator will "age and drift" due to changes in the crystal structure, and the output frequency will drift cumulatively and irreversibly.
· Unit: Usually pay attention to the annual aging rate, ±PPM/year (also marked by month or day).
＞ Selection Inspiration
· The first-year aging rate of high-quality crystal oscillators is generally ±1ppm ~ ±3ppm. Usually the drift is large in the first year, and then it tends to be stable. OCXO can even achieve ppb level.
· For long-term operation and unattended equipment such as communication base stations, smart meters, and industrial network gateways, it is recommended to give priority to crystal oscillators with low aging rates.
04 Phase noise and jitter
Keywords: Is the signal clean?
The clock signal must not only be "accurate", but also "pure". In high-speed communication and precision measurement, signal tremors and noise will bring hidden dangers.
Phase noise and jitter are key indicators to measure the purity of crystal oscillator signals, which directly affect transmission quality and anti-interference ability.
Figure: YXC Data Sheet - Phase Noise & Jitter (Yellow Highlight)
＞ Index Definition
① Phase Noise:
· Definition: An index to measure the purity of the clock signal in the frequency domain, indicating the random phase disturbance around the frequency, reflecting the phase instability of the signal in the spectrum.
· Unit: dBc/Hz. The lower the value, the purer the signal spectrum and the stronger the anti-interference ability.
② Jitter:
· Definition: An index to measure the uncertainty of the edge time of the clock signal in the time domain, indicating the time deviation between the actual clock edge and the ideal position.
· Unit: picosecond (ps) or femtosecond (fs) RMS. The smaller the value, the more stable the signal and the more reliable the data transmission.
＞ Selection Recommendation
· For high-speed serial interfaces such as PCIe, SerDes, ADC/DAC, low jitter can improve the quality of the eye diagram and reduce the bit error rate. It is recommended to give priority to differential output crystal oscillators (LVDS, LVPECL, HCSL).
In scenarios with extremely high requirements for signal-to-noise ratio, such as 5G communications, phased array radar, and high-precision visual measurement, high-performance crystal oscillators with low phase noise, such as TCXO, VCXO, and OCXO, should be given priority.
