How modern scopes can save you time

Keysight Technologies Australia Pty Ltd
Wednesday, 22 September, 2010

We are all doing more with less. We’re being asked to shorten deadlines, design products and shorten repairs. For digital designers and test and measure situations, one of the key tools to make this all happen is an oscilloscope.

If you haven’t bought a new oscilloscope in the last five years, you might be surprised at some of the timesaving capabilities the latest models offer. Some are enhancements of traditional capabilities - things like limit testing have been around for decades, but new features in today’s oscilloscopes can greatly enhance their value.

Some of the time-saving capabilities are things that you may have never thought of - for example, having the scope decode an I2C serial waveform versus manually decoding it yourself.

When most people are buying oscilloscopes, they typically look at specifications like bandwidth, sample rate and memory depth to determine what scope to purchase. However, increasingly there is a fourth specification that people look at - update rate. How can update rate be a timesaving feature?

The most obvious reason is it allows you to debug your design with more confidence. Infrequent glitches are schedule killers - they are difficult to find and drive down to root cause.

But with a fast update rate, you are much more likely to find the issue. Finding an infrequent anomaly that is keeping your design from working is often one of the most difficult things to do.

Today’s latest generation of oscilloscopes offer many applications that allow you to tailor your scope from a general-purpose debug tool to one that is customised for your application. These timesaving applications include serial applications that automatically decode the link for you; no more counting ones and zeros trying to decode the link yourself.

However, decoding is only the start. Some oscilloscopes offer hardware-based decoding of the link. This offers two key benefits:

  • Having the oscilloscope do the decoding in hardware for you has zero impact on the update rate. When the decoding is done in software, it often has a performance penalty on the update rate of the scope;
  • The scope is still responsive. There is no waiting after you change the time base for oscilloscope to ‘crunch’ back through the data. It is done in real time.

Many scopes today also offer a lister view of the decoded data. This view, similar to a logic analyser’s lister view, provides a high-level overview of all the data captured. It allows the designer to go from the physical layer (the waveforms) to the protocol layer (the link transactions).

Being able to search through this data and step between each of the found items is another timesaving feature that allows the user to quickly look through the deep memory records that many of today’s best scopes offer (see Figure 1).

Figure 1: Searching the serial data of a CAN bus.

Segmented memory is another example of a timesaving application. Segmented memory allows the user to capture only a specific window of time but capture that window multiple times.

This allows the user to get a much longer capture time, by keeping the oscilloscope from capturing data during long periods of signal dead (or inactive) time.

Segmented memory is most useful when working with bursty or infrequent data.

While segmented memory can be used with any trigger condition, it is extremely powerful when tied to a serial trigger as it allows the user to capture thousands of specific serial packets and then step through them.

Figure 2 shows a controller area network (CAN) error that was triggered on and then captured using segmented memory. Note the timestamp on the scope - over 12 minutes of time elapsed between the first error and 2000th error.

Figure 2: Using segmented memory, this figure shows over 12 minutes’ worth of time captured around a CAN error..

As mentioned earlier, limit testing has been around for some time. Limit testing allows you to create a ‘gold standard’ waveform that you can test against (Figure 3) - the scope will then show you violations against that gold standard.

Figure 3: Hardware accelerated mask testing allows you to gain quick confidence in your design.

This is great for manufacturing test or just any development need where you want to test your product against a known requirement (limit).

In the past, to get a statistically significant amount of data, limit testing has traditionally required minutes, or even hours of test time.

However, there is a new timesaving feature available in some oscilloscopes today that can greatly speed your time to insight - hardware acceleration. By accelerating the mask testing via hardware you can test up to 100,000 waveforms per second, giving you the ability to quickly find anomalies.

While waveform update rate and oscilloscope applications are more tied to a specific task you are trying to accomplish, there are also many useful model features in new oscilloscopes that are focused on saving you time.

For example, ‘pushable’ knobs. Pushable knobs are like a button built into the knob. They allow you push the button to do things like automatically set the trigger level to 50%, or snap back to the trigger on the horizontal time base.

They can also allow you to switch to ‘fine’ mode (sometimes called ‘vernier’) to dial in your vertical or horizontal settings.

‘Quick action’ buttons are another example. These allow you to define an action that the scope will do when you push that button - things like save, print, recall or freeze the display.

Upgradeability is another feature that is often overlooked when specifying an oscilloscope but can save you a great deal of time, and money, in the future. It allows you to add a new feature to your oscilloscope without having to send the scope in to the factory or, even worse, having to purchase an entire new scope.

Things like software applications are a great example of upgradeability and are what most people think of when they think of upgrading their scope.

But there are also some hardware capabilities that can be upgraded easily. For example, the ability to upgrade from a traditional digital storage oscilloscope to a mixed signal oscilloscope that gives you 16 additional logic channels integrated into your scope - all without taking your scope off the bench or undoing a screw.

Finally, one of the last timesaving features is directly tied to how often you use the oscilloscope. If you are like most engineers, you don’t use your scope 10 hours a day, five days a week. While an oscilloscope is probably the tool you use most often in your test and measurement tasks, it can require a small amount of time to refamiliarise yourself with it, especially with functions that you may not use frequently.

One way to do that is to have a printed-out manual next to the scope at all times. This is certainly one method, but often the manual is lost or you have difficulty finding the information you are looking for.

An even better approach is to offer help directly on the scope. Some scopes today do that in a very intuitive, innovative way, providing you quick access to what each button does through a pop-up dialog when you hold down a button. This allows you to get fast, targeted help, without pulling out a manual or opening a web browser.

In the end, we are all looking for ways to do our work faster and more efficiently. Although not a traditional area to think about saving time, advances in oscilloscope capability have taken the typical oscilloscope and enhanced it, providing a much more efficient tool.

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