Crystal
A crystal turns electrical energy into mechanical vibration and back, locking a circuit to a precise frequency. It gives microcontrollers, radios, and clocks the timing accuracy they need.
Quartz is piezoelectric: squeeze it and it makes a voltage; apply a voltage and it deforms. Cut to a precise thickness, the slab has a natural resonance the surrounding circuit can lock onto.
In plain terms
Like a tuning fork that rings at a single, exquisitely stable note. Tap it electrically and the whole system can dance to its rhythm.
Also called: XTAL, quartz.
Why designers use it
- Provide a stable clock for a microcontroller's CPU.
- Generate accurate baud rates for UART, SPI, and CAN.
- Tune the carrier of a wireless transceiver.
- Drive a real-time clock that keeps date and time across power loss.
Best for
- MCU main clock
- USB / Ethernet timing
- Wireless reference
- Real-time clocks
Key specifications
- Frequency range: 32.768 kHz – 200 MHz
- Tolerance at 25 °C: ±5 ppm – ±50 ppm
- Aging: ±1 – ±10 ppm/year
- Load capacitance: 8 – 22 pF (Set by motherboard caps)
- ESR: 10 – 200 Ω
When not to use it
- Where size and BOM cost matter and a built-in MCU oscillator is good enough.
- Across mechanically stressed or vibration-heavy environments — a MEMS oscillator is tougher.
Common mistakes
- Skipping the load capacitors a crystal datasheet specifies — startup will be flaky or impossible.
- Routing the crystal trace through noisy areas of the board.
Where you will find it
- A quartz wristwatch keeps time accurate to seconds-per-month because a tiny tuning-fork crystal vibrates exactly 32,768 times per second — the watch IC counts those vibrations and ticks one second every 2¹⁵ of them.
- GPS satellites broadcast time from atomic clocks, but the receiver in your phone uses a temperature-compensated crystal oscillator to lock onto those signals — without that crystal, your map would be off by miles.
- Every Wi-Fi and Bluetooth radio depends on a reference crystal so accurate that two devices made by different companies can hop the same frequency channels in lock-step.
A short history
The piezoelectric effect—the generation of an electric charge by mechanical stress in a crystal—was discovered by Pierre and Jacques Curie in 1880. In 1921, Professor Walter Guyton Cady of Wesleyan University first demonstrated a quartz crystal used to control and stabilise an oscillator's frequency, exploiting the crystal's extremely high Q factor (typically 10,000–100,000) to produce frequency stabilities impossible with LC circuits alone. AT-cut quartz crystals, developed at Bell Labs in the 1930s, minimise the temperature coefficient near room temperature, achieving stabilities of ±20 ppm without oven control. Today quartz crystals regulate the system clocks of virtually every digital device from watches to base stations.
Good to know
- 32.768 kHz is exactly 2¹⁵ Hz — divide by 2 fifteen times and you get a 1 Hz tick. That's how every quartz watch keeps time.
- A quartz crystal is a mechanically resonant slab cut from the same mineral that makes up most beach sand — but its frequency stability beats any electronic oscillator by a factor of 1,000.
- The crystal in your GPS receiver has to be accurate to 1 part in 100 million — drift more than that and the satellite math collapses.