Which One Fits your Need: TCXO or OCXO?

A crystal oscillator is an electronic oscillator circuit that uses a quartz crystal to create an electrical signal with precise frequency. It is often used in precision timing applications (clocks) to provide a stable clock signal for digital integrated circuits and stabilize frequencies for radio transmitters and receivers.

Crystal oscillators are subject to influence from environmental factors, like humidity, temperature, pressureand vibration. Temperature Compensated Crystal (Xtal)Oscillators (TCXO) and Oven Controlled Crystal (Xtal) Oscillator (OCXO) are quartz crystal-based modified oscillatorsthat limit the level of these influences.Both provide exceptional short-term stability with main differences in the complexity of the electronic components in the circuit and the effects of crystal aging.Withadvancements in crystal oscillator technology, the gap between TCXOs and OCXOsis shrinking, making it potentially difficult to determine which one is best suited for your needs. 

TCXOs

Temperature in the external environment can affect the crystal oscillator's ability to maintain its frequency output stability. TCXOs were developed to easily adapt to changes in temperature in various external environments.A majority of TCXOs contain a voltage control mechanism called a voltage-controlled crystal oscillator (VCXO).It includes a temperature sensor that monitors temperature changes andapplies a correctional voltage to the voltage control pin. The counter-balance circuitry of the VCXOallows the TCXO to provide stable frequency. 

The temperature coefficient of the capacitors used to adjust frequency affects the temperature coefficient of the crystal, which can lead to problems with adjustments for crystal aging and long-term stability. The change in the temperature coefficient can be ignored inlower precision TCXOs butrequires adjustment for higher precision TCXOs.TCXOs counteract crystal aging by allowing the frequency to be reset periodically through external adjustments. The level of accuracy required determines the time needed between calibration resets, but general recommendations are every six months to a year. However, shorter periods are needed for higher levels of accuracy. Issues with the crystal cannot be corrected, which makes the crystal design and manufacturing a crucial and difficult element.

OCXOs

The quartz crystal inside an OCXO is heated by an oven-like device. The oven has precise temperature control and heats the crystal to its turn over temperature, maintaining it throughout the duration of its use. This helps keep the crystal temperature constant and prevents fluctuations from external temperature changes that lead to compromises in its desired frequency stability. 

The cut of the quartz crystal affects OCXO performance. There are two types used: AT cut and SC cut. AT cut crystals are more widely used in OCXOs and are preferred for a wide temperature range. SC cutcrystals provide a higher level of frequency stability and precision compared to AT cut and are more suitable for elevated operating temperatures. It should be noted that OCXO crystals are subject to about a quarter of the crystal aging sensitivity that TCXOs undergo. 

Comparison and Applications

Size and Complexity

OCXOs are typically larger than TCXOs due to the mechanical components they consist of: IC, heater and controller, and the crystal. TCXOs are smaller and simpler since they only consist of IC and the crystal. This makes OCXOs more suitable for operations that require a high degree of stability and TCXOs better for smaller devices that need to be portable. 

Cost and Power Consumption

OCXO requires higher power consumption because they need a longer warm up period to reach the precise temperature before they function. They also need a constant heat supply to maintain the “oven” temperature. This makes them costlier than TCXOs, which require a significantly shorter warmup period and less power to maintain its temperature. 

Applications

OCXOs are best for operations that require better frequency stability and precision clocking, like the 5 GNSS Constellations (GPS, QZSS, BEI Dou, GALILEO, and GLONASS). Applications include any operation requiring GPS, like military data links and test equipment, but OCXOs are too bulky to be used in battery-powered devices. Due to TCXO’s high level of performance and smaller size, you are likely to find them in many of today'ssmart phones, GPS devices, and other base station applications.

For a more comprehensive list of applications, please check our OXCO devices by clicking hereor our TCXO devices by clicking here

Summary

OCXOs are better for communication/network applications that require high precision frequency and provide better long-term stability. TCXOs are preferred when size and power are critical to the application. They are more economical and provide reasonable stability. These tend to be better for portable or battery operated devices.