Developments In Microcomputer-Compensated Crystal Oscillator Technology

By Steve Fry, Greenray Industries, Inc.

When an application requires a precision frequency control device, temperature-compensated crystal oscillators (TCXOs) provide several advantages over ovencontrolled crystal oscillators (OCXOs). Microcomputer-compensated crystal oscillators (MCXOs), a subclass of TCXOs, achieve improved frequency vs. temperature stability through the use of digital compensation.

The most obvious benefit of compensated oscillators is a significant reduction in supply current (power) required. A typical OCXO requires a power drain of 5 W from the power source when turned on. Even ultra-low power OCXO designs may draw 1.5 W when they are first powered up.

This is in contrast with TCXO designs, which draw a meager 0.006 W. This low power consumption is constant and does not change with time or temperature. While the frequency stability of a TCXO is not equal to a precision OCXO, even low-power analog compensation can provide stabilities that begin to rival a low-cost miniature OCXO.

Adding digital temperature compensation can improve the frequency stability of the low-power compensated oscillator to be as good as, or in some cases better than, a small OCXO. This is achieved with only a modest increase in input power to around 0.05 W. A wide variety of types and techniques of digital compensation have evolved over the years, each with unique features and benefits.