Mastering Phase Noise Measurement In Oscillator Production

By Emily Newton

Manufacturers producing products containing oscillators must understand how to measure phase noise and reduce it if necessary. Failing to take phase noise measurements as a part of the quality control process can reduce the item’s performance and reliability.

Phase noise occurs when the phase of an oscillator’s output signal in the frequency domain fluctuates. Why does that matter, and which phase-noise measurement techniques should people use?

How To Measure Phase Noise With The Most Common Techniques

Manufacturers and others with a dedicated interest in electronics quality control use several strategies. Knowing how to measure phase noise with these options is the best way to determine which one is most appropriate for the present needs.

Using A Spectrum Analyzer

A spectrum analyzer can help people learn more about phase noise measurements. It shows the signal amplitudes of different radio frequencies as a spectrum. In addition to seeing noise represented, people will notice short-duration events and complex waveform patterns. They can then study that data to determine if the phase noise is within or outside of expected boundaries.

Spectrum analyzers vary slightly by manufacturer, but most have dedicated buttons that help people make frequency, span, and amplitude measurements. Most require a short warm-up period to work properly before use, so individuals must always read the manufacturer’s instructions carefully for the best results.

Relying On The Direct Spectrum Technique

This option requires feeding the tested device’s signal into a phase noise analyzer to measure the oscillator’s power spectral density in terms of its frequency. These phase noise measurements offer a well-understood and straightforward process that is best suited for sources with relatively high noise levels. However, other measurement methods work better when someone needs to measure in-phase noise that is very close to that of a drifting carrier.

Measuring With The Two-Channel Cross-Correlation Method

The two-channel cross-correlation method requires a comparative approach. People using it introduce a second channel while working with the tested device. They then use a signal-processing tool to identify the noise shared between the two products and narrow it down to only the one being tested.

Checking Phase Noise With A Phase Detector

Another comparative method involves using a phase detector to see how an oscillator’s output differs from a stable reference signal. The phase detector can determine the variation between the two sources, allowing people to see whether the oscillator’s data meets or exceeds quality control minimums.

Introducing A Delay Line

People also can check the phase noise associated with manufactured oscillators by running a delay line test. This approach requires examining the signal of the tested item against a comparison signal and adding a delay line to one of the two transmitted signals. Analyzing the difference between the delayed and original signal allows for measuring the phase noise.

Subtracting The Residual Noise

A final way to measure an oscillator’s phase noise is to determine the signal noise created by other components. Subtracting out that residual noise allows people to identify the phase noise linked to the oscillator alone. Power supplies, input clocks, amplifiers, and other parts of a product can contribute to the overall phase noise. However, once people understand what’s coming from the oscillator versus elsewhere, they can take an accurate phase noise measurement.

Designing And Manufacturing Low-Noise Oscillators

Phase noise can cause signal attenuation, data loss, and communication challenges. These issues are especially important to address when using oscillators in mission-critical applications. Factors such as vibrations and deviations in gravitational force equivalents can increase the likelihood of phase noise measurements higher than what quality control metrics allow. However, people can reduce such instances by choosing high-performance oscillators that can consistently offer low-noise operations.

One program specifically addresses the world’s need for such items by exploring opportunities to use photonic oscillators that offer tunable outputs across the whole spectrum. Those participating in this initiative will investigate the feasibility of applications up to 110 gigahertz to accommodate the needs of future systems operating in high-frequency bands.

Finding And Fixing Issues

Pinpointing identified problems during the quality control process helps manufacturers discover if the issue involves just one item or every one coming off an assembly line. Leaders may also want to train more staff in how to measure phase noise.

 

Signal noise from crystal oscillators falls into one of three categories:

• Power supply noise: This type occurs when a power supply line behaves like an antenna, releasing pulsations that manifest as phase noise. However, workers can be proactive by exploring ways to stop those pulsations from coming into the power supply or absorbing them.
• Output line noise: The output line also can act as an antenna, meaning the signal from the oscillator becomes phase noise. Mitigating those effects requires making the output waveform and output line conform to requirements that make it difficult for the signal to get released as noise.
• Oscillator noise: Finally, since the oscillator contains integrated circuits and wiring, those components can become phase noise sources. However, a stable power supply can eliminate such problematic conditions, as can consistent oscillator performance.

Knowing about noise sources is as important as knowing how to measure phase noise. Employees may eventually notice large product batches fail quality control checks due to excessive phase noise. If so, the company may need to optimize its processes to manage the problem. While no one can prevent issues 100% of the time, quality control goes a long way in minimizing event occurrences, reducing liability, and keeping customers loyal.

Suppose the quality control failures began occurring relatively recently. In that case, leaders must investigate what has happened with this batch of products, discover the problem, and remedy the situation.

Phase Noise Measurements Align With Quality Control

People overseeing quality control in an oscillator production facility must consider aspects such as employee training, high-tech equipment used in the manufacturing process, and the designs of oscillator-containing items. Taking phase noise measurements allows staff to determine whether individual items pass or fail quality control checks.

In the latter cases, professionals can perform some of the measurement methods mentioned above to gauge the phase noise severity. Then, they can go further to determine what caused the problem and how to prevent it in the future.