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 are many external factors that can 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
- Stray-capacitances
- Output loads
Additionally, here are 5 other 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 crystals oscillators were developed to hold the crystal at a constant 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.
Related: Can a Crystal Oscillator Operate Outside of the Specified Temperature Range?
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. This is due to the fact that quartz is a piezoelectric material. The cool part about that is 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.
Luckily, mechanical vibrations can usually be avoided or solved easily. We wrote another in-depth article on how phase noise can be reduced in highly dynamic environments.
4. Heat Buildup
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.
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, which leads to a drift in the frequency output. One possible solution to this problem is to use a regulated power supply.
Related: How to Maintain Frequency Stability in Crystal Oscillators
The Simplest Way to Ensure Frequency Stability
Yes, you can avoid each of the above problem sources with individual devices… but why not solve as many issues as possible with a single device?
Using a high quality ultra-stable oven controlled crystal oscillator (OCXO) may be the easiest and most effective solution. Ultra-stable OCXOs (sometimes abbreviated as USOs or MROs) are specifically designed to address 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 from influencing the oscillator’s stability.
Need an Ultra-Stable Oscillator?
If you think a high quality ultra-stable OCXO might be a smart, simple choice for your application, check out our groundbreaking ultra-stable OCXO series oscillators. They’re ready and waiting to take your application to the next level.
Browse our line of high-performance crystal oscillators or download the ultra-stable OCXO datasheet for more info.
