Crystal oven
A heated quartz oscillator, sometimes referred to as quartz oven and English Oven Controlled Crystal Oscillator (OCXO ) is a quartz oscillator, which is housed in a heated and temperature controlled chamber. The quartz oscillators are crystal oscillators used in a small, but significant application for precise thermal dependency of the resonant angular frequency, which is also referred to as a thermal drift. By controlling the temperature of the quartz resonator and the oscillator circuit to a value above room temperature, the oscillator circuit frequency can be stabilized and thus a higher accuracy than without heating can be achieved.
General
In contrast to temperature compensated crystal oscillators ( TCXO) which minimize the disturbing temperature-induced frequency variations by means of a temperature measurement and calibrated correction values is minimized in a heated quartz oscillator, the temperature influence by active heating and maintaining the temperature at a constant high level. Applications of heated quartz oscillators include simple frequency standards and digital frequency counter, where a higher accuracy than non-stabilized quartz crystal is required, and at the same time a lower accuracy than atomic clocks can be tolerated.
The typical operating temperature is 75 ° C, but can be depending on the specific type and application in the range of 30 ° C to 85 ° C. and is coordinated with the crystal manufacturer. As quartz cuts for quartz used in the furnace, the AC-cut and SC-cut may be used. A selection criterion for the temperature to increase the stability of operation is that point where the crystal frequency or no as small as possible as a function of the temperature gradient has. A further improvement is obtained when power transistors rather than heating resistors are used as a heating element in the oven. The reason is that the heat losses of the bipolar power transistors is direct proportional to the current, while heater resistors there is a quadratic dependence. The quadratic dependency makes it difficult to keep the temperature constant.
The short-term stability of the heated quartz oscillators for several seconds is about 10-12, the long-term stability can be achieved in the range of 10-8, which is to be reached in a few days depending on the type operating according to a few hours. 10-8 corresponding to the relative value of a maximum deviation of 1 Hz with an oscillator frequency of 100 MHz.
The data of some oscillators are summarized in the following table of comparison: