Quartz Crystal / Resonator
Timing
A passive component that uses the piezoelectric effect of quartz to provide a precise frequency reference for oscillators in timing circuits.
Schematic symbol
Crystal / resonator
How quartz crystal / resonator appears in a circuit diagram.
Types & variants
Key specs
Frequency
Hz (MHz, GHz)The resonant frequency at which the crystal oscillates. Common values: 4MHz, 8MHz, 16MHz, 25MHz, 32.768kHz (for RTC).
Load capacitance
pFThe capacitance required for the crystal to oscillate at the specified frequency. Typically 8pF, 10pF, 12pF, 15pF, or 18pF.
Frequency tolerance
ppmHow much the actual frequency can deviate from the nominal value. Typical values: ±10ppm to ±100ppm for general use, ±1ppm to ±5ppm for precision.
Frequency stability
ppmHow much frequency changes with temperature. ±20ppm to ±100ppm for standard, ±1ppm to ±10ppm for TCXO.
Equivalent series resistance
Ohm (Ω)The resistive loss of the crystal at resonance. Lower ESR means better performance. Typically 10Ω to 100Ω.
Drive level
μWMaximum power the crystal can handle without damage. Typically 100μW to 1mW.
Markings
Through-hole: Frequency printed on case (e.g. 16.000 for 16MHz). SMD: Frequency code (e.g. 16.0 for 16MHz) or full frequency printed. Some crystals have a load code (e.g. 'A' for 8pF, 'B' for 12pF, 'C' for 15pF).
Standard values
Common frequencies: 32.768kHz (real-time clocks), 4MHz, 8MHz, 10MHz, 12MHz, 16MHz, 20MHz, 24MHz, 25MHz, 40MHz, 50MHz, 100MHz. Standard load capacitances: 8pF, 10pF, 12pF, 15pF, 18pF.
How to choose
1) Determine required frequency for your application. 2) Check if temperature compensation is needed (TCXO for precision). 3) Select appropriate load capacitance for your circuit design. 4) Ensure frequency tolerance meets timing requirements. 5) Verify drive level won't damage the crystal.
Pinout & package
2 leads (non-polar, can go either way). Packages: HC-49/S (through-hole), SMD packages: 2.0x1.6mm, 3.2x2.5mm, 5.0x3.2mm, 8.0x4.5mm. Some crystals have 4 pins (2 for crystal, 2 for case connection).
Example circuits
- Microcontroller clock source
- Real-time clock (RTC) circuit
- Communication system clock (UART, SPI, I2C)
- RF oscillator for wireless modules
- Digital logic timing circuit
Common failures
Frequency drift (aging), failure to oscillate, damaged from excessive drive level or mechanical shock. Cracks or discoloration on the package indicate physical damage. May go completely silent (no oscillation) when failed.
How to test
Use an oscilloscope to check for oscillation across the crystal with appropriate circuit (with load capacitors). Frequency should be within specified tolerance. A multimeter can check for continuity (should show some resistance, not open/short), but won't verify oscillation.
Substitutes
Ceramic resonators (less stable but cheaper), silicon oscillators (more stable but more expensive), PLL-based clock generators (for multiple frequencies). Must match frequency and load capacitance for direct replacement.