temperature compensated crystal oscillator (TCXO)
In contrast to the oven-controlled crystal oscillators, Oven Controlled Crystal Oscillator( OCXO), the temperature-compensated crystal oscillators, Temperature Compensated Crystal Oscillator (TCXO), work with thermistors. These temperature-dependent devices are used to generate a temperature-dependent correction voltage to control the oscillator.
The correction voltage is applied to the crystal oscillator and reduces its temperature-dependent frequency changes. Normally, the correction voltage is applied to a capacitance diode in the crystal oscillator, which can be used to change the frequency slightly. With this technique, stability values of 0.1 ppm, corresponding to `10^-7`, are achieved.
TCXO oscillators have a relatively long temperature hysteresis; it takes some time for the temperature compensation to settle during rapid temperature changes. This hysteresis requires some effort for the development of highly stable TCXOs; among other things, the temperature dependence of the frequency setting elements of trimming capacitors or potentiometers must also be taken into account.
If the temperature compensation is analog, then they are Analog Temperature Compensated Crystal Oscillators( ATCXO), if it is digital, then they are Digital Temperature Compensated Crystal Oscillators( DTCXO), and if it is controlled by a microcomputer, then they are Microcomputer Compensated Crystal Oscillators( MCXO). TCXOs are used wherever power savings are required and where no warm-up time, as required by the OCXO, can be accepted.