Temperature Compensated Crystal Oscillators (TCXO)

A temperature compensated crystal oscillator (TCXO) is a crystal oscillator that uses a compensation network of thermistors. The oscillator is designed to produce a correction voltage that reduces the frequency deviation due to variations in the temperature. The thermistors detect variation in the ambient network and make the appropriate corrections to the voltage that is applied to the crystal. These oscillators are often used in data communication and telecommunication applications.

A crystal oscillator is an in electronic circuit which uses the mechanical resonance of a physical crystal of piezoelectric material along with an amplifier and feedback to create an electrical signal which has a very precise and accurate frequency. The crystal oscillator is a very accurate version of an electronic oscillator. This frequency is used to keep track of time such as in quartz wristwatches, to provide a stable clock signal for digital integrated circuits, and to stabilize frequencies for radio transmitters. Crystal oscillators are a popular and common source of time and frequency signals. The crystal that is used is often called timing crystal.

While selecting a TCXO you need to consider the oscillation frequency and the total frequency stability. Measured in ppm, the total frequency stability is the maximum value by which a frequency varies, from the mean or the nominal value, for changes in temperature and supply voltage. You also need to consider the connector that is used. The output can be given as a sine waveform or a square waveform. The square wave logic outputs are: TTL, CMOS, HCMOS and ECL. The crystal must have a low jitter and a low noise feature.

There are several packaging options for these devices as they are available as surface mount, flat pack, through hole, waveguide assembly or as a connector. Surface mount technology (SMT) adds components to a printed circuit board (PCB) by soldering component leads or terminals to the top of the board. Through hole technology (THT) mounts the components by inserting component leads through holes in the board and then soldering the leads in place on the opposite side of the board. Oscillators that are modules or boards are also available. Connectorized devices attach with either coaxial or radio frequency (RF) connectors. Waveguide assemblies are made of a hollow metallic conductor with a rectangular, elliptical, or circular cross-section. Flat pack (FPAK) units come with flat leads and in assorted body sizes and pin counts.

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