Temperature-Compensated Crystal Oscillators – TCXO’s

A temperature compensated crystal oscillator (TCXO) is a specialized type of crystal oscillator that provides an even higher level of stability and accuracy when required for particular electronic devices. In a standard crystal oscillator unit, oscillation frequency variations occur in response to increases in temperature. This instability of frequency can seriously impair the overall function of the electronic device. Essentially, a TCXO actively counteracts the effect of any temperature variations on the crystal oscillator’s frequency stability. These crystal oscillator units are most commonly found in high-temperature environments.

TCXOs are prized for their frequency stabilization properties, including how they are able to resist and counteract even fairly significant increases in external temperatures. In a TCXO, its temperature compensation network, also known as a thermistor network, identifies temperature changes outside of the specified range and initiates a frequency stability mechanism in response. The Temperature change causes the thermistors to vary, which causes a change in the equivalent capacitance of network. This in turn changes the capacitance load on the crystal, causing a change in the frequency of the oscillator.

Even though standard crystal oscillators are valued for their resistance to changes in temperature and maintenance of specified frequencies, they may still be subjected to temperature variations. A TCXO efficiently stabilizes the oscillator’s frequency level in response to temperature changes, which allows this type of crystal oscillator to be used in settings with variable temperatures without sacrificing performance or incurring significant operating expenses.

Distinctions between the common types of TCXOs are based on the type of mechanism that each oscillator uses to counteract temperature changes. The most common types of TCXOs include the analog digital TCXO, digital TCXO, DCXO and MCXO.

A voltage-controlled temperature compensated crystal oscillator (VCTCXO) is a type of TCXO that maintains and stabilizes its oscillation frequency by relying on the application of an analog voltage in response to temperature increases. The voltage applied to the VCTCXO is exactly inverse to the temperature change, which maintains the TCXO accuracy.

A TCXO offers solutions to the primary issues with quartz crystal oscillators, including crystal aging and frequency stability. Instead of encasing the crystal within an oven to protect it, the TCXO identifies temperature changes and stabilizes the frequency through the application of the voltage current at the exact inverse of the variation in temperature. In addition, TCXOs are intended to be recalibrated approximately every six to 12 months, which protects against premature crystal aging. That is why TCXOs are used in high-quality mobile phones, tablets, GPS navigation devices and portable radios.

Crystal oscillators are susceptible to frequency drift in response to prolonged and significant temperature changes outside of their specified range. Even though a crystal oscillator may be able to function temporarily outside of its specified temperature range, it is not recommended for the performance and longevity of the oscillator unit and device.

Although oven-controlled crystal oscillators (OCXOs) and TCXOs are both heat-related oscillation devices, a TCXO provides enhanced frequency stability protections against temperature increases and is much smaller than an OCXO. TCXOs are ideal for portable electronic devices that require a stable frequency source.

OCXOs are larger than TCXOs and standard crystal oscillators because they require a heater for the oscillator. The TCXO is more compact because it does not operate with an oven and insulation layer. Also, the TCXO may not even require a seal enclosing the oscillator package. The package sizes of the TCXO vary according to their function, but they are relatively small compared to other oscillator options.

OCXOs may consume a significant amount of power because the heater in the OXCO typically requires power from an additional source than the oscillator itself. An increase in the OXCO’s internal temperature after starting up will reduce the amount of power required for operation. In terms of the TCXO circuit design, the additional circuitry needed for a TCXO to sense and respond to temperature results in greater power dissipation than that of a standard oscillator.

Unlike an OXCO, a TCXO is intended to be reset or recalibrated at regular intervals. The specifications for the individual device will describe the recalibration requirements. This process helps stave off crystal aging, which is an issue for the longevity and stability of other crystal oscillators.