Crystal oven

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A crystal oven is a temperature-controlled chamber used to maintain constant temperature of electronic crystals, in order to ensure stability of operation of an oscillator known as an Oven-Controlled Crystal Oscillator or OCXO. It is typically used in broadcast and measurement applications where precise frequency of oscillation is critical to proper circuit operation.

The crystal is mounted within a thermally-insulated enclosure; the enclosure also contains one or more electric (resistive) heaters. Closed-loop control is used to modulate the heater and ensure that the crystal is heated to the specific temperature desired. Because the oven operates above ambient temperature, the crystal or oscillator within usually requires a warm-up period after power has been applied. During this warm-up period, the frequency may not be fully stable.

Because of the power required to run the heater, oscillators using crystal ovens require more power than oscillators that run at ambient temperature and the requirement for the heater, thermal mass, and thermal insulation means that oscillators using ovens are physically larger than their ambient counterparts. However, in return, the oven-controlled oscillator achieves the best frequency stability possible from a crystal. Achieving better performance requires switching to an atomically-stabilized technique such as a rubidium standard, caesium standard, or hydrogen maser. A much cheaper alternative is to discipline a crystal oscillator with a GPS time signal, creating a GPS Disciplined oscillator (GPSDO). Using a GPS receiver that can generate accurate time signals (down to within ~30ns of UTC), a GPSDO can maintain oscillation accuracy of 10^-13 ppm for extended periods of time.

In crystals for nonlinear optics, the frequency is also sensitive to temperature and thus requires stabilization, especially as the laser beam heats up the crystal. Additionally fast retuning of the crystal is often employed. For this application, the crystal and the thermistor need to be in very close contact and both must have as low a heat capacity as possible. To avoid breaking the crystal, large temperature variations in short times must be avoided.