Crystal Frequency Stability

Δf = f0 × ppm × 1e-6

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Result
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Formula

Δf = f0 × ppm × 10⁻⁶

Description

Crystal oscillator frequency stability is specified in parts per million (ppm), indicating the maximum frequency deviation from the nominal value due to temperature variation, aging, and manufacturing tolerance. A 10 MHz crystal with ±20 ppm stability can deviate by ±200 Hz. Over temperature, crystals follow a parabolic curve centered near 25°C. AT-cut crystals (the most common) achieve ±10 to ±50 ppm over the industrial temperature range (-40 to +85°C). Temperature-compensated (TCXO) and oven-controlled (OCXO) oscillators achieve much tighter stability.

Variables

  • Δf — Frequency deviation from nominal (Hz)
  • f0 — Nominal crystal frequency (Hz)
  • ppm — Stability specification in parts per million

Practical Notes

Typical stability by oscillator type: crystal (XO) ±20-100 ppm, TCXO ±0.5-5 ppm, OCXO ±0.01-0.1 ppm, atomic clock ±0.0001 ppb. For UART communication, frequency accuracy must be within ±2% for reliable data transfer. USB requires ±500 ppm at low speed and ±50 ppm at high speed. Crystal aging adds ±3-5 ppm/year.

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