XOs – Non-Compensated Crystal Oscillators
Non-compensated crystal oscillators employ no correction or control to reduce the frequency variation over temperature beyond the intrinsic crystal stability. However, ‘non-compensated’ is a bit of a misnomer since AT-cut crystals exhibit an S-shaped cubic frequency vs temperature curve which can hold the frequency variation below a few parts per million for modest temperature excursions and below a few tens of parts per million for extreme temperature variations. The angle of the crystal cut determine the temperature curve and the manufacturer selects the most appropriate curve for the design temperature range.
Typical AT-Cut crystal curves for various cut angles.
Simple XOs are a good choice when the stability requirements are not stringent because they are less expensive, smaller, and more reliable than TCXOs and OCXOs. Since non-compensated oscillators require few selected components or critical adjustmenst, the designer may choose to design his own. Here are a few helpful .pdf files for the designer:
|Tiny CMOS Crystal Oscillator||cmososc.pdf|
|Low Distortion Crystal Oscillator||xtalosc.pdf|