What Is a Crystal (Quartz)?
A crystal (quartz) is a piezoelectric component that produces a very stable, precise frequency reference. It's the "metronome" of digital systems and forms the basis of timing.
How Does It Work?
A quartz crystal is piezoelectric: when voltage is applied it vibrates mechanically, and when it vibrates it produces voltage. This vibration happens at a very specific frequency and is quite stable against temperature.
Why Is It So Stable?
The crystal's vibration frequency depends on its physical cut and is barely affected by external factors. So it's thousands of times more accurate and stable than a resistor-capacitor oscillator.
| Property | Value |
|---|---|
| Stability | Very high (ppm) |
| Typical frequency | kHz – MHz |
| Operation | Piezoelectric vibration |
Load Capacitance
A crystal needs a specific load capacitance to vibrate at the correct frequency; this is provided by two small capacitors. The wrong value causes the frequency to drift slightly; so a capacitor matching the load capacitance specified in the crystal's datasheet must be chosen. For a simpler alternative, a ceramic resonator can be used.
Where Is It Used?
Microcontroller clocks, RTCs (32.768 kHz), USB/Ethernet references, radios and communication devices.
Common Mistakes
- Load capacitance: the wrong capacitor shifts the frequency.
- Layout: the crystal must be near the MCU with short traces.
- Mechanical shock: a crystal is vibration-sensitive; a hard shock damages it.
Frequently Asked Questions
What's the difference between a crystal and an oscillator?+
What does ppm mean?+
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