Editor’s note: Here is a useful blog previously published on EDN by my colleague Martin Rowe, EDN editor, Test & Measurement.
Every electronic circuit has some amount of noise. If you're working with sensitive analog circuits, then noise can ruin your day. Noise can have several sources such as from external EMI, switching power supplies, clocks, even active and passive components. Because noise is often random, you typically can't simply look at it with an oscilloscope to determine its source. Fortunately, you can use math tools found in many oscilloscopes to characterize noise.
Arthur Pini, a longtime engineer at LeCroy (now Teledyne LeCroy) has written an article that walks you through the steps to characterize noise using the time domain, frequency domain, and statistical domain. You can apply many of the techniques described in Analyze noise with time, frequency, and statistics to analyzing jitter, should you actually find yourself working on high-speed digital designs.
Pini opens with an overview, showing a noisy signal and some of the tools he uses to characterize it.
The top left trace in the screen image (click the image to enlarge) above shows a time-domain view of band-limited Gaussian noise. The trace below that shows the noise in the frequency domain, which is its power spectral density. On the right, Pini then use a histogram that presents a statistical view of the random noise. Histograms approximate the noise using a probability density function. The screen image also shows several measurement parameters derived using math functions that quantify the waveforms. Pini then delves into the details of how to use these tools, explaining the information they provide and how to use that information to your advantage.
Pini has written extensively for Planet Analog's sister publication EDN on how to use oscilloscopes. This article on measuring noise brings his total to 30, and he's not done yet. See Oscilloscope articles by Arthur Pini for the complete collection. Three of his article feature ten useful oscilloscope tricks so keep an eye open for them.
—Martin Rowe covers test and measurement for EE Times and EDN. Contact him at firstname.lastname@example.org