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TCXO, Temperature Compensated Crystal Oscillator

As the name indicated a temperature compensated crystal oscillator provides a means of counteracting the frequency change caused by temperature change in a crystal oscillator.

The letters TCXO stand for Temperature Compensated Xtal Oscillator - Xtal is short from crystal and implies a quartz crystal resonator. The TCXO module is able to provide considerably improved performance over that of a standard crystal oscillator, especially in terms of frequency stability over a temperature range.

By measuring the temperature and applying a correction voltage to a VCXO, the frequency stability over a temperature range is considerably improved whilst keeping costs low - using an oven controlled crystal oscillator, OCXO would be considerably more costly and much larger in size.

Often a wide range of TCXOs of varying frequencies, supply voltages and packages is available from many distributors, enabling these electronic components or modules to be used in many general electronic designs, RF circuit designs, etc.

Temperature performance of crystal oscillator

Crystal oscillators are able to provide a much better level of performance than that provided by LC resonator circuits. Nevertheless crystal oscillators are still affected by temperature.

The angle of the cut and other aspects of the quartz crystal have a major impact on the performance.

As a result special cuts are defined and one known as the AT cut is the most widely used for these and many other quartz crystal RF applications. This gives a good level of performance for RF circuits in terms of suppression of unwanted modes of vibration as well as the frequency range available, and also the temperature stability.

Despite this, AT cut crystals on their own cannot meet the requirements for many applications and temperature compensation is required if they are to perform satisfactorily over the required range - often 1 - 70°C at elast is needed.

The effects of temperature are, to a large degree, repeatable and definable. Therefore it is possible to have an electronic design to compensate for this. By adding additional electronic components to the basic oscillator, it is possible to considerably reduce the effects caused by temperature changes: a temperature compensated crystal oscillator, TCXO.

TCXO solution

TCXO adjusts the frequency of the oscillator to compensate for the changes that will occur as a result of temperature changes. To achieve this, the main element within a TCXO is a Voltage Controlled Crystal Oscillator, VCXO. This is connected to a circuit that senses the temperature and applies a small correction voltage to the oscillator as shown below.

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