What is frequency drift?

What is frequency drift in crystal oscillators? What causes it? How can it be eliminated?

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- everything RF

May 25, 2023

Frequency drift is an undesired change or variation in the frequency of an oscillator from its nominal value over time. Frequency drift can be caused by numerous factors, including electronic component aging, changes in temperature that alter the piezoelectric effect in the crystal oscillator, problems with voltage regulators which control the bias voltage to the oscillator, and other causes such as mechanical vibration & electromagnetic interference (EMI). The EMI can introduce noise or disturbances that influence the frequency stability. Frequency drift is typically measured in Hz/s. The absence (or very low level) of frequency drift can be regarded as frequency stability.

Frequency drift may not necessarily be linear and can occur in either direction (i.e., increasing or decreasing in frequency). It usually occurs in devices that generate frequency signals or process them like oscillators, clocks, transmitters, receivers, and repeaters.

Frequency drift can affect a system's performance. For example, in the case of a transmitter, the frequency drift can lead to a radio station drifting into an adjacent channel, thereby causing unauthorized interference and violating regulations. This is why Frequency allocation regulations specify allowed tolerances for oscillators used in certified products/devices. Frequency drift can also cause errors in data transmission, due to loss of synchronization issues, or reduced signal quality.

How can we eliminate frequency drift?

In the case of crystal oscillators, frequency drift can be eliminated by using temperature-compensated voltage-controlled crystal oscillators (TCVCXOs), oven-controlled crystal oscillators (OCXOs), digitally controlled oscillators (or Numerically controlled oscillators), and phase-locked loop (PLL). All these devices can be used to compensate for frequency drift.