Oven Controlled Crystal Oscillators

A crystal oscillator is an in electronic circuit which uses the mechanical resonance of a physical crystal of piezoelectric material along with an amplifier and feedback to create an electrical signal which has a very precise and accurate frequency. The crystal oscillator is a very accurate version of an electronic oscillator. This frequency is used to keep track of time such as in quartz wristwatches, to provide a stable clock signal for digital integrated circuits, and to stabilize frequencies for radio transmitters. Crystal oscillators are a popular and common source of time and frequency signals. The crystal that is used is often called timing crystal.

However, the performance of crystal oscillators is usually affected by temperature changes which occur during prolonged use. This problem is generally solved by heating the crystals in a series of precision ovens to a temperature that is above the working temperature of the crystal. The crystal is enclosed in a small insulated container along with a heating element and a temperature sensor. This configuration is designed to keep the crystal at a constant temperature, one which is well above the temperature of its working environment; generally the desired target temperature is about 70–80 degrees Celsius.

In many applications this process can improve the frequency stability of the crystal by a factor of ten or more. This process makes the crystal more stable, more resistant to aging effects, jittery and it also gives a low phase noise. OCXO are used in timing devices for signal generators, oscilloscopes, PLLs, satellites, radio communications and mobile phone systems, etc.

OCXO have to be warmed up for a few minutes before it stabilizes. Important parameters are: oscillating frequency in hertz, total frequency stability (which tells the amount of deviation from the nominal frequency), vibration rating, input voltage and current, output type (sine or square wave) and the operating temperature.

These devices can be PCB or chassis mounted and are available in frequency values from a few hertz to gigahertz. Manufacturers designate them either alphanumerically like MOA, MOB, and MOD or as a series like CO 18, CO 115, etc.


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