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OCXO basics | OCXO types | AT cut,IT cut,SC cut difference

The page describes OCXO basics and OCXO types. It compares OCXO types viz. AT cut, IT cut and SC cut and mentions difference between AT cut,IT cut and SC cut.

Definition: The term OCXO stands for Oven Controlled Crystal Oscillator. As the name suggests the crystal oscillator which keeps its frequency output stable regardless of its surrounding ambient temperature variation is known as OCXO.

As we know TCXO is used to have frequency output based on temperature. Though TCXO has temperature compensated frequency output, it has lower frequency stability. Due to this limitation, OCXO having higher frequency stability is used in applications requiring high stability.

OCXO working operation

It is widely used in applications requiring very high frequency stability in oscillators, synthesizers, transceivers, signal generators, signal analyzers etc.

OCXO working operation

The figure-1 depicts inside of OCXO crystal oscillator type. As shown it consists of oven controlled circuit, temperature sensor and crystal oscillator. The improvement in stability is due to the fact that OCXO maintains constant temperature of crystal regardless of ambient temperature variation.

This is achieved with the help of oven based heater control circuit. Based on temperature sensed by the thermistor or any other temperature sensor, heating element increases or decreases the temperature of the crystal. OCXO keeps temperature constant based on closed loop feedback network. By keeping temperature constant, frequency stability of oscillator can be improved.

OCXO Frequency Response

As shown in the figure-2, OCXO of SC cut type has better frequency stability over wide temperature compare to IT cut and AT cut types.

OCXO Types | AT cut, IT cut, SC cut

Following are the types of OCXO crystal oscillator.
• AT cut
• IT cut
• SC cut
The figure-2 depicts OCXO working with frequency response of different types.

OCXO AT cut

Following are the features of AT cut crystal type.
• The AT cut is made from Y bar at 350 theta rotation.
• It is entry level OCXO type.
• It offers good stable performance over wide temperature range. from -55oC to 125oC.
• It offers frequency output from 0.5 to 300 MHz.

OCXO IT cut

Following are the features of IT cut crystal type.
• Like SC cut, it is also double rotated crystal type and hence used in high stability applications.
• Offers frequency output from 0.5 to 200 MHz.
• It has upper turning point between 85oC to 105oC.

OCXO SC cut

Following are the features of SC cut crystal type.
• It offers double rotation which is defined by theta of 34.11 degrees and phi of 21.93 degrees.
• It offers frequency output from 0.5 to 200 MHz.
• The cutting method is difficult and hence will lead to higher labor cost.
• The stresses observed in AT cut type is reduced or eliminated using second rotation in φ direction.
Refer AT cut versus SC cut crystal types>> and advantages and disadvantages of SC cut crystal over AT cut>>.



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