Let’s Talk Oscilloscopes and Their Capabilities Beyond Basic Measurements

This article was originally published in 2019.

In a previous article¹, we touched on the basics of oscilloscopes. In this earlier article, we discussed the purpose of oscilloscopes, basic measurements, basic functions and controls, and how to safely use them without causing harm to the user or equipment under test (EUT). In this article, we will leave the basics behind and explore more of the state-of-the-art advanced cool features, functionality and specifications that are available in today’s oscilloscopes. If you’re not currently involved in taking advanced measurements with oscilloscopes and are unfamiliar with their advanced capabilities, please stay tuned. You may be surprised at just how far the technology has advanced.

In the world of oscilloscopes, there are basically two different classifications. One is deemed “mainstream” and the other is called “high-end.” This article won’t differentiate the two but will describe the capabilities of each in general. Just be aware that mainstream oscilloscopes usually have less “horsepower” than the “high-end” types and they usually cost much less (~$1000 – $2000 versus tens of thousands of dollars). The good news is that features that were once considered top-of-the-line are now considered mainstream. Mainstream oscilloscopes contain advanced features except in affordable packages. For really serious users needing the most advanced and sophisticated features for very precise measurements, the high-end type of oscilloscope is the most appropriate. Just be prepared to pay a premium for oscilloscopes with such advanced features. They are significant investments for most any organization.

So just what are these advanced capabilities and why have they been developed? Let’s answer the second part of this question first.

These new capabilities have been developed out of necessity. As technology advances and product development times shorten, product developers need faster, more accurate, more repeatable information from our test instruments. If it isn’t already, the mantra within the product development community should be “faster, more accurate, more repeatable, easier to use.”

As an example of the need for advanced features, consider the voltages used to power the chips we’re currently using in our designs. They are continually decreasing and getting smaller. Some signals, such as these, are getting smaller and other ones used within our products aren’t. Because of this, designers need to be able to look at these small signals in the presence of larger ones in order more accurately analyze noise margins. Designers require low noise measurement capability at the smallest vertical per division setting. To fulfill this need, some high-end scopes are shipping with higher bit vertical resolution capability, such as 10-bit vertical resolution.

Circuits are also getting faster. The problem with fast operating circuits is that if the bandwidth of the oscilloscope is too low, it will not resolve high-frequency changes, the amplitude captured is distorted, edges vanish, and important details are lost.

Related to the bandwidth issue is rise time. Critical details of faster pulse transitions are lost if the scope’s rise time is not quick enough, therefore the rise time capability of today’s oscilloscopes is getting shorter. When specifying a new oscilloscope to purchase, verify that its rise time capability is less than one-fifth that of the fastest rise time of any signals you intend to measure. For example, in order to properly measure a signal with a 5ns fast-edge rate, choose an oscilloscope with at least a 1ns rise time.

Another element that is driving the latest advanced features found in today’s oscilloscopes is the need to shorten product development lead times. Long product development times cost more money than shorter ones. Product development times can be reduced if designers can quickly get accurate information needed to solve a problem and then move onto the next. For instance, product designers are more productive when we can employ real-time acquisition and avoid time-consuming post-processing of data. Once data is collected and analyzed for one task, designers need to be able to quickly reconfigure the oscilloscope for the next task and then quickly capture data for it. In order to fulfill this need, some vendors are producing x-in-one instruments (where x = six, seven, etc.) that can be easily configured with various plug-in modules that allow these devices to perform as an oscilloscopes, logic analyzer, spectrum analyzer, voltmeter, counter/totalizer, serial bus analyzer (protocol analyzer), function generator, arbitrary waveform generator, or power analyzer.

It is because of the above reasons (and some others) that we’re seeing advancements in oscilloscope capabilities. Here are a few of some of the more important advanced capabilities found in these new powerful instruments:

• Higher Bandwidths: As previously mentioned, oscilloscopes should have enough bandwidth to faithfully represent the signal being tested (usually five times the maximum signal bandwidth). Some present day higher-end scopes are employing bandwidths in the 23 to 110 GHz range.
• Faster rise times: See discussion above. Note that proper testing of TTL and CMOS logic devices may require an oscilloscope with a 300 to 400 ps rise time capability.
• Higher sampling rates (Samples per second, S/s): A higher sample rate increases resolution and ensures intermittent events are seen. The best measurement results are obtained with scopes that have a sample rate that is at least five times the highest frequency component of the signal to be measured. Some quoted sample rates found on the latest high-end scopes are 500 MS/s, 2 GS/s, 128 GS/s, 256 GS/s per channel.
• Increased number of channels: The channels have to be accurate and the scope should have enough of them. One use of this enhanced feature is measure amplitude and phase differences between multiple channels. Caution: The number of channels in use could negatively impact sample rate (sample rate decreases as more channels are added). Consult the owner’s manual of the oscilloscope for specific details regarding this limitation.
• Deep capture memories: Deep capture memories allow for longer tests and more data to be collected and analyzed during these tests. This feature is specified in the number of points in a complete waveform record. The greater the record length the better. New search mode capability allows one to easily find only the events of interest located within a full record of memory.
• Better user interaction: This includes more productive real-time calculations that eliminate the need for additional post-processing of data (FFT, integrate, differentiate, log, exponent, square root, etc.), large touch-screens that allow for better viewability of captured waveforms, automatic measurement setup, ability to automate waveform measurements, powerful waveform navigation and analysis (zoom and pan, play and pause, marks, search and mark, advanced search), and other extra functions that shorten the time to find correct answers.
• Specialized triggers: Specialized triggers are now included in high-end scopes that make it easier to detect and trigger on non-ideal (runt) and other distorted pulses.
• Power measurements: Provides automated measurement capability in development of devices such as switched-mode power supplies. Includes power quality, switching loss, harmonics, safe-operating area, modulations, ripple, slew rate, etc.
• Automated compliance testing: Many scopes enable the user to perform compliance testing, jitter and eye-diagram analysis. This functionality includes the ability to correctly verify the functionality of USB 3.x interfaces, PCI Express 3.0, DDR4/LPDDR4, etc.

This brief article covered just a few of the latest advanced features and capabilities found in today’s oscilloscopes. If the reader wants to dig deeper and is interested in learning more about these advanced features please check out references 2 through 5 listed below.

References

1. MacArthur, D., “What Every Electronics Engineer Needs to Know About: Oscilloscopes,” In Compliance Magazine, June 2018.
2. “Advanced Oscilloscope Measurements and Analysis,” Keysight Technologies Blog Post, September 1, 2016.
3. “12 Things to Consider When Choosing Your Next Oscilloscope,” Tektronix.
4. Hockett, M., “Oscilloscopes – Once high-end features now becoming mainstream,” Evaluation Engineering, December 2018.
5. Hockett, M., “Top of The Class – Innovations empower high-end oscilloscopes to serve demanding applications,” Evaluation Engineering, April 2019.