Phase noise, phase noise, phase noise.
If you’re involved with the design and implementation of communication systems, you most likely hear the term “phase noise” all the time (maybe more times than you’d like).
There’s a good reason for all this phase noise chat. It’s one of the key factors that determines the overall success or failure of your radar or communications application. It’s even more important in intense environments where strong vibration or g-force is a concern.
Why is maintaining low phase noise such a concern in these applications and environments? And how can you solve the problems associated with the effects of phase noise? By the end of this article, you'll know why and how you should decrease phase noise in your applications.
Phase noise is typically measured as the frequency stability within a crystal oscillator. If you're unfamiliar with them, a crystal oscillator is basically the main component that creates and transmits the radio frequency signal in radars and communication systems, microwave systems, military applications, and many other applications.
Vibrations from many different sources, even very small vibrations (micro-vibrations), can cause phase noise and jitter in the crystal oscillator. This inhibits the quality and stability of the signal produced by the oscillator, making the overall communication of the device more difficult.
Other causes of phase noise include g-forces and acceleration sensitivity.
Related: The Ultimate Guide to Understanding Phase Noise
Phase noise can cause problems in various applications. Let's take a look at two different microwave systems and how they’re negatively affected by phase noise.
Direct down-conversion is a fairly basic microwave communication receiver with a simple circuit. It’s a single mixer containing a local oscillator (LO) that converts the incoming radio frequency signal down to a very low frequency. This low frequency is then applied right to an analog-to-digital converter for processing.
The problem is that the RF input frequency is often nearly the same as the frequency of the oscillator. This makes the conversion process easier for some pesky phase noise to slip into the signal. It's even more likely to happen if there’s a weak signal strength.
A similar type of problem occurs in radar systems. Instead of a direct RF input, radars pulse a specific frequency and then measure the change of each returning frequency pulse. Each pulse change is related to the velocity of an object in the radar’s view by making use of the doppler effect. Objects moving very slowly will return a pulse that is very close to the original frequency of the pulse sent out.
The returning signal must be converted to a very low frequency to uncover the precise information of the velocity change. Like direct down-conversion, this low frequency conversion can cause phase noise to negatively affect the data received.
For many applications, a crystal oscillator alone cannot provide enough output power to perform at optimal quality. It will sometimes be necessary to call on amplifiers to help the little oscillator emit a stronger signal.
But as it often happens in engineering, solutions can cause new problems. Amplifiers can be great at boosting the signal power of an oscillator, but they can also cause unwanted phase noise that hinders the oscillator’s performance.
Amplifiers, along with all other electronic devices, add 1/f noise (pink noise) to an input signal. Basically, even if you have an oscillator with low phase noise qualities, amplifiers can completely replace their higher phase noise qualities with the oscillator's low phase noise. Of course, that’s no good.
If you're down for some fun, consider learning about the different colors of noise.
The first and most important step to eliminating phase noise is in your designs is to find a high quality, low phase noise oscillator from a trusted supplier. Doing this is the easiest and most effective way to eliminate phase noise from its root source.
Especially in military, aerospace, or extreme-environment applications, high g-force levels and heavy vibrations can cause a lot of unnecessary phase noise in oscillators. Luckily, there are g-compensated oscillators specifically designed to take on the heavy vibrations and forces of gravity and prevent any phase noise issues.
Consider checking out the Poseidon 2 series OCXO. Poseidon 2 is the world's best low phase noise, low-cost OCXO on the market when subjected to dynamic random vibration conditions.
As far as amplifiers go, the 1/f (pink) noise is caused by random and thermal charge movement in the channel of the device. Amplifiers are manufactured with a Gallium Arsenide (GaAs) pHEMT process. The FET devices in the process tend to have high 1/f noise rates due to their high electron mobility. But GaAs bipolar devices typically offer a much lower 1/f noise, which also means less phase noise. Use a GaAs HBT process amplifier to significantly reduce the phase noise in your application.
Our high-performance, low phase noise oscillator features the world's lowest phase noise performance when subjected to dynamic random vibration conditions. It's perfect for eliminating phase noise in extreme vibration and g-force environments.
Download your copy of the Poseidon 2 datasheet >>