Crystal Oscillators Explained: The Importance Of PPM

Crystal Oscillators: The Heartbeat of Real-Time Clocks

Crystal oscillators are at the core of real-time clocks (RTCs), providing the stable and precise frequency necessary for accurate timekeeping. These oscillators use the mechanical resonance of a vibrating crystal of piezoelectric material (usually quartz) to create an electrical signal with a very precise frequency. This frequency is used to keep track of time.

  • Stability: Crystal oscillators offer exceptional stability, meaning they maintain a consistent frequency over time and under varying environmental conditions.
  • Accuracy: They provide high accuracy, crucial for applications where precise timing is key, such as in data logging and time-sensitive transactions.
  • Reliability: Crystal oscillators are known for their longevity and reliability, making them ideal for long-term applications in various industries.

Crystal Oscillators in Everyday Use:

  1. Smartphones: Keeping accurate time for alarms and timestamps, even when powered off.
  2. Computers and Laptops: Managing file timestamps and scheduling system updates.
  3. Household Appliances: Enabling programmable cooking times and automated functions.
  4. Wearable Fitness Trackers: Accurately tracking workout durations and sleep patterns.
  5. Gaming Consoles: Synchronizing time-based game events and playtime tracking.

Crystal Accuracy in PPM

In digital technology, accuracy remains fundamentally important. The crystal oscillator, an unassuming yet critical component, sits at the heart of this precision. Its role is to provide the heartbeat for digital circuits. The accuracy of these crystals comes from their measurement in PPM – parts per million. Crystals, serving as clocks for digital circuits, have their accuracy defined in ppm (parts per million), where a lower value indicates higher time measurement accuracy.

What is PPM and Why Does It Matter?

PPM, standing for parts per million, measures the accuracy of a crystal oscillator’s timekeeping ability. A lower PPM value means a more accurate clock. This measurement proves crucial in applications requiring precise timekeeping, like communication systems, GPS devices, and computers.

The Real-World Impact of PPM Values

Consider a crystal with 50 ppm.

Number of seconds in a day = 24 hours * 60 minutes * 60 seconds = 86400

(50/1000000)*86400 = 4.32 seconds a day (about 26.28 minutes a year)

so, a crystal with 50 ppm will have a maximum error of 26.28 minutes a year

Have you wondered why a real-time clock uses 32.768kHz?

Real-time clocks typically use a 32.768 kHz crystal. Why this frequency? Its binary compatibility holds the answer. This frequency matches exactly 2^15 (32768) Hz, making it perfect for dividing using a 15-stage counter to achieve one-second intervals. This approach streamlines the circuitry needed for timekeeping, demonstrating the elegance and efficiency of digital logic.

2 to the power of 15 yields 32768.

32.768kHz can be divided using a 15-stage counter to derive 1-second timing.


In conclusion, the precision of crystal oscillators, measured in PPM, significantly influences timekeeping accuracy in digital circuits. Understanding this metric and the design rationale behind crystal frequencies like 32.768 kHz offers deep insights into the complex world of electronic timekeeping.