RF engineers are always trying to improve the performance of the systems they work on. A perfect, 100% stable signal which never deviates from the intended frequency will probably never be attainable in reality; the toll that the physical environment and time will take on a crystal remains a fact of life.
But that doesn’t stop us from always working towards getting as close to possible to that ideal. Both of these challenges can be mitigated by selecting a high-quality quartz crystal oscillator. Picking the right one for the job depends on the application for which it is being used, as well as other factors like the amount of power available.
In this article, we will make the case that for those who are trying to minimize the effects of aging and improve stability without using a lot of power, a temperature-compensated crystal oscillator (TCXO) might be the right solution.
The 2 Most Important Criteria: Crystal Stability and Aging
Two of the most important criteria for evaluating crystal oscillator performance are crystal stability and aging. Stability refers to the ability of a crystal to maintain a steady, consistent frequency, while “aging” is a term that describes how the frequency of a crystal will change slightly over the course of its usable lifetime. Aging will slowly occur even in very well designed systems, but there are multiple environmental and design factors which can accelerate the aging process. These include contamination of the crystal lattice, as well as dust and other foreign bodies touching the surface of the crystal. Other factors include:
- Drive levels of the crystal (how much power dissipates through the crystal)
- The types of gas in the air surrounding the crystal
- Ambient temperatures
We’ve mentioned in previous articles the benefits of oven-controlled crystal oscillators (OCXO). For applications requiring strong, stable and ultra-stable signals, OCXOs do excel in that respect. But OCXOs are not always the best fit for every project. For one thing, they typically have longer warm-up times than other types of oscillators. Another significant factor is that many OCXOs require comparatively high amounts of power, and sometimes that just isn’t an option.
So, what is the solution for those who want to fix the problems of stability and aging without drastically increasing their power consumption?
Enter: The TCXO
A Temperature-Compensated Crystal Oscillator performs the same function as an OCXO— nullifying the potentially harmful effects of ambient temperature on the crystal— but does it in a different way. Rather than shielding the crystal itself within an oven, a TCXO is able to sense changes in the temperature in which the crystal is performing and respond by changing the frequency of the crystal output to offset the increase in heat or cold. This is accomplished by altering the voltage applied to the crystal at an exact inverse of the temperature change. TCXOs are also designed for periodic recalibrations to reduce the effects of crystal aging. (Typically, a TCXO will be reset every 6 to 12 months.)
Common applications for a TCXO include:
- Mobile phones and tablets
- GPS devices
- Reference clocks
- Portable radios
TCXOs typically perform much better than oscillators without any form of temperature correction or protection. Some advantages a TCXO enjoys over an oven-controlled oscillator are shorter warm-up periods, and significantly lower power consumption. While OCXOs are generally considered the best for reducing phase noise, aging and improving stability, for many applications, it just makes more sense from an economic and technical standpoint to go with a TCXO
Is a TCXO right choice for your next project? Take a look at the datasheets for our world-class TCXO designs to find the perfect solution for eliminating the effects of crystal aging and instability in your systems.