Here’s the scary thing…
Even if you sit for hours upon hours trying to set a precise initial frequency of an oscillator, it’s still going to drift and the oscillator will not be able maintain that frequency over the full course of its use. In this post, you’ll learn the MANY sources of frequency instability and why an Ultra-Stable OCXO may be the fix-all solution.
There’s many external factors that have a negative impact on an oscillator’s intended frequency. Variants in a circuit alone can determine an application's frequency fluctuation. Examples include:
- Circuit components
- Transistor parameters
- Supply voltages
- Output loads
Additionally, here are 5 more common ‘frequency eaters’ that are out there waiting to suck the frequency accuracy of your quartz oscillator right out of your applications:
1. Operating Temperature Range
Swings in environmental temperature have a significant impact on quartz crystal frequency. To combat this effect, ovenized crytals oscillators were developed to hold the crystal at a contsant elevated temperature. The better the oven can control the temperature of the crystal, even as the ambient temperature changes, the better the frequency stability of the OCXO will be.
2. The Active Device's Operating Point
The operating point of the active device in the circuit must be carefully selected to work in the linear portion of its characteristics. Otherwise, there might be variations in the transistor parameters. This will ultimately lead to frequency instability.
3. Mechanical Vibrations
Mechanical vibrations are a very common problem when it comes to frequency stability and phase noise problems. Luckily, these problems can usually be easily avoided or solved. This is due to the fact that quartz is a piezo-electrical material. The cool part about that is that you can apply a voltage to a crystal and it will oscillate or vibrate. The bad news is that you can apply a vibration and it will create a voltage, which shows up as phase noise in the frequency offset of the induced vibration.
We recently wrote a great, in-depth, article on how phase noise can be reduced in highly dynamic enviroments.
4. Heat Build Up
Naturally, as a circuit operates for an extended period of time, the temperature of the circuit will begin to increase. This heat increase will cause frequency determining components (capacitors, inductors, resistors, etc.) to change. The change of overall frequency is usually slow in this case, sometimes making the instability less noticeable.
Here’s another thought… Can a crystal oscillator operate outside of its specified temperature range?
5. The Operating Power Supply
Any alteration in the power supply load coupled to the tank circuit may spark a change in the effective resistance of the circuit. Of course, this is what leads to a drift in the frequency output.
A possible solution to this problem is by using a regulated power supply.
Yes, you can avoid enduring each of the above problem sources with individual devices… But why not try and cover as much ground as possible with a single device?
Using a high quality, ultra-stable OCXO (sometimes abbreviated as USO or MRO) may be the easiest and most effective solution. Ultra-Stable Oven Controlled Crystal Oscillators (OCXO) are specifically designed to take on the many possible causes of frequency instability in your circuits and applications.
Some higher quality Ultra-Stable OCXOs even provide a very high stability vs. temperature feature that prevents fluctuating temperatures to influence the oscillator’s stability.
If you think a high quality ultra-stable OCXO might be a smart, simple choice for your application…check out our new groundbreaking ultra-stable OCXO series oscillators. They’re ready and waiting to take your application to the next level.