A temperature-controlled chamber utilized in maintaining the quartz crystal present in the electronic crystal oscillators (at constant temperature) is known as a crystal oven. Its main aim is to cease any changes in the frequency because of varieties in encompassing temperature. An oscillator of this category is known as Oven-Controlled Crystal Oscillator (OCXO; Here “XO” is an old short form for “crystal oscillator”). This kind of oscillator gets the greatest frequency stability possible using a crystal. They are used generally to manage the frequency of cellular base stations, radio transmitters, equipment for military communications as well as in measuring frequency precisely.
Description
Quartz crystals have found its wide use in electronic oscillators to manage the frequency generated precisely. The frequency of vibration of a quartz crystal resonator depends completely on its dimensions. When there is a change in temperature, it leads to the thermal expansion of the resonator. This results in the change of frequency of the signal produced. The coefficient of thermal expansion is very low in quartz, still, the change in temperature is the major cause of the difference in frequency in the oscillator.
The oven comes with the crystal and some electrical heating elements. It is also thermally insulated. Other electrical equipments present inside the circuit are likewise helpless against temperature float, thus, the whole oscillator circuit is enclosed inside the oven. A thermistor temperature sensor in a closed-loop control circuit is utilized to make sure that the oven is kept at a desired precise temperature as well as to manage the power of the heater. The oven is said to start its work above ambient temperature and because of it the oscillator generally requires a warm-up time after the power is supplied to reach its operating temperature. The frequency will not have the full rated stability during this warm up time.
The operating temperature chosen for the oven is that at which the slope of Crystal’s Frequency Vs. The temperature curve is Zero. SC-cut (Stress-Compensated) or AT- crystals are utilized. The SC-cut has a wide range of temperatures over which the near-zero temperature coefficient is accomplished and along these lines lessens warmup time. Instead of resistance heating elements, power transistors are used for the heaters. The power output of these transistors is not proportional to the square of the current but only to the current. This linearizes the gain of the control loop.
One of the temperatures which is common for a crystal is 75 degree Celsius. But depending on the setup it may vary between 30 to 80 degrees Celsius.
Most standard commercial crystals are indicated to an ecological temperature of 0 to 70 degrees Celsius and the industrial ones are generally specified to -40 to +85 degrees Celsius.
This was all we have regarding OCXO Oscillators. Hope you liked reading it. Brands that manufacture them are ABRACON and ECS Inc. Do give a check to these manufacturers using the links as provided.
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