Today's Question of Interest: Will the crystal oscillator operate outside its specified temperature range?
This is a common question and the short answer is ….wait for it…Yes, but it's complicated.
If, for example, an oscillator is specified over 0 to 60 oC, it will most likely perform without any issues over -40 to 85 oC; however, it is possible that it will fall outside its specified stability. This may not matter if the application needs just a stable frequency rather than an accurate frequency.
Below are test results of the same oscillator being tested over two different temperature ranges. The one on the left is from -20 to 70 oC. As you can see it is very stable. The one on the right is from -40 to 85 oC. It is no longer as stable at the extreme temperatures. If temperature stability is vital in your system then operating within specifications is necessary.
It is not recommended to operate a crystal or oscillator outside of its specified temp range for other reasons as well. The most notable reason is the greater frequency drift that is possible due to the increased temperature extremes. Another phenomena that can occur is accelerated crystal aging, which can impact stability as well as frequency accuracy.
One of the most serious problems that can occur is activity dips. In an OCXO, this could simply be due to running the oscillator above the oven’s setting temp; where the oven will shut off as shown below.
Activity dips can also cause the oscillator to stop oscillating completely at a specific temperature. Manufacturers usually design around this problem, but can’t guarantee it beyond the specified range.
For system designers being careful about how much power is being used, an OCXO will also usually draw more current to keep the oven going at colder temperatures. The power consumption of an oscillator may be acceptable at -20 oC but not at -40.
So, to sum it all up, yes you can but it isn’t recommended.
The best course of action is to know the needed temperature range ahead of time and stick with it if possible. If you run a unit outside of manufacturer’s specs anything can happen, from the merely annoying to the system crippling.
Want to learn even more about what makes these devices tick? Check out this guide to understanding the types of quartz crystals inside OCXOs.