Oscilloscopes: The EE’s Stethoscope

Oscilloscopes are like the electricity to your house. You don’t give it much thought until a storm knocks it out. The entire electronics industry can’t function without oscilloscopes. But this equipment is such a constant and so consistent, we sometimes forget it’s there.

Semiconductor Engineering spent time with three Test & Measurement (T&M) industry stalwarts to talk about Oscillocopes: Past, Present and Future — National Instruments, Keysight, and Teledyne Lecroy. These machines have evolved from Tektronix’ circa-1982 classic 2000-series (see fig. 1, below), wholly analog with 3-inch CRTs and 100MHz of bandwidth to today’s all-digital top of the line from Tek and Keysight (formerly Agilent, formerly HP).

Fig. 1: Then…Tek model 2213 60MHz scope.

Fig. 2: And now…Tek’s new DPO70000SX series.

Bill Driver, senior product manager at National Instruments in Austin, is a relative newcomer in the oscilloscope history’s span. But he remembers fondly his first experience as an EE major in college 20 years ago, getting to be among the lucky ones to get in to the “power lab” that had a Tektronix digital scope, not analog as the other two campus labs had.

“I lived through that time when everyone was saying, ‘Old school analog is best, digital has problems’,” Driver said. He ended up going to work for Tektronix in the New England area right out of school. When you called on engineers in their labs, you heard an earful about the tactile feedback of the knob on an analog scope, about the resistance to any scope that was going to run wonky unreliable Windows, he said. “Why would you want Bill Gates inside your scope? I need to turn the knob.”

Today, many oscilloscopes output to giant displays—any one the engineer would like. National Instruments’ new PXIe-5164 is modular, with no display, and can interface to a soft panel, where an engineer can adjust the ‘scope triggers.

“Now we can see the benefits of digital far, far outweigh the benefits of analog,” he said. But that wasn’t always the case. And the silicon powering the bandwidth gains and subsequent high sampling rates was nowhere near today’s.

“Back then, 4 GHz was cutting edge. That was the TDS7404. The news of 6Ghz scope coming was a really big deal,” Driver said. “Then I worked for Lecroy (now Teledyne Lecroy). I moved to New York. They had the 100GHz sampling scope. That was unheard of.”

National Instruments, in these latest PXIe oscilloscopes, continues to leverage a variety of off-the-shelf components. Tek and Keysight remain at the top in this critical custom silicon, along with Teledyne Lecroy.

“The earliest digital oscilloscopes had 6-bit analog-to-digital converters. ADCs have resolution of 2^Nth bit,” explained David Maliniak, technical marketing communications specialist at Teledyne Lecroy. “Thus, a 6-bit ADC yielded 64 discrete levels of vertical voltage quantization. Teledyne LeCroy’s HD4096 technology uses 12-bit ADCs to deliver 4096 discrete quantization levels. That’s 16X better than the old 6-bit instruments.”

Fig 3: The advantage of 12-bit ADCs.

Teledyne Lecroy has done some re-thinking of the critical signal paths within the instrument, improving the front-end amplification chain and getting gains in a given scope channel signal-to-noise ratio (SNR). Its HDO series scopes also use variable-gain amplifiers downstream to refine the signal, on top of sophisticated mathematical filtering.

Keysight runs its own Indium phosphide fab. All of its 16-100GHz ADCs are built in Indium phosphide, which enables the world’s fastest ADC. Then, large custom digital ASICs accomplish certain signal processing capabilities. And they maintain silicon germanium, gallium arsenide and other BiCMOS manufacturing capabilities to keep at engineers’ disposal.

Software takes the stage
Brad Doerr, Keysight’s director of R&D for oscilloscopes and protocol analyzers, highlights another key silicon technology—post-sample-acquisition digital signal processors (DSPs), coupled together with the gains that much more sophisticated on-board software brings.

“The compliance applications, the protocol decoding capabilities, the advanced triggering, the jitter analysis you get today,” said Doerr. “All this is software. In the last 10 to 15 years, the software (engineered into today’s oscilloscopes) has really taken over and enabled some incredible things.”

Which brings us back to that change from all analog scopes to digital in the late 1990s.

“In the late 1990s, you definitely heard that push back,” Doerr said. “But now, there is no doubt. The digital capabilities are so superior.”

Digital scopes meant vastly superior I/O, storage and software capabilities, as Doerr points out. Take triggering, for example. “In the old days, you used to move a horizontal line up and down and create a triggering level. So you could display what you capture at that trigger. Nowadays you use your finger and touch the screen and draw a box. ‘If the signal comes through this box, capture and store it.'”

That opens the door to a number of new technical opportunities. “You can do really cool and complex things with that,” Doerr continued. “You have zone triggering. As an EE, that is exceptionally powerful. If I can create a trigger for something that only happens once in a blue moon, I can go home at night and come back in the morning, and maybe that mouse trap caught a mouse.”

Such capabilities only came about in about the last two years. “That’s one of the most exciting and different things about the ‘scopes market vs. say nine years ago when I first started working in it. People have no idea how much software is involved.”

Doerr noted that is what today’s oscilloscopes and their much more advanced software add for industry standards. It’s part of the reason Keysight grew its business in Colorado, close physically to where the National Institute of Standards and Technology (NIST) folks do their work.

“Say you are designing to the new USB 3.x interface. Do you have sufficient bandwidth and sampling depth? You can purchase software for your ‘scope that will tell you if what you built is meeting the spec of the standard. And all the compliance applications are traceable back to NIST. I’m an engineer and I can print a certificate from my oscilloscope that tells me, and tells me my boss, whether the device is in compliance with the global standard,” he said.

Customers validate compliance to PCI Express, DDR2, 3 and 4, the low power DDR standard, and “of course a whole bunch of variances of Ethernet,” he said. NIST, based in Boulder, “produces traceable standard equipment that we purchase from them, that allows use to insure compliance. Every few years that all has to be calibrated and certified. If it’s not traceable to NIST you can really never conclude that you are done,” Doerr noted.

Since the dawn of oscilloscopes time, these T&M companies have given EEs jitter analysis, an understanding of what Doerr dubs, for the layperson, a signal’s left-right wiggling. “Now, we can tell the engineer if that jitter is deterministic, or data-correlated, if it’s random or not random. Jitter analysis has really blossomed in oscilloscopes.”

Doerr has been with Keysight since first signing on with HP 28 years ago. He had gotten an EE undergrad degree, but a master’s in software. “I’m sure glad I have that software background,” he said.

The future…as NI sees it
NI’s Driver talked about what’s to come for oscilloscopes, in terms of how they are used and when.

“At its core, what do you buy an oscilloscope for?” said Driver. “You buy it to solve problems you don’t know you have.”

And who each of these companies talks to in order to discuss solving those problems is changing. That’s driven by the RF and the wireless explosion, as well as the needs of aerospace and defense today.

“There used to be this clear-cut differentiation. If I’m NI, I’m going to call a test manager. Tek [ Tektronix ] is going to call an engineering design manager. There is a hypothetical wall between the two.

“We recognize that. Picture the classic ‘Design V’ diagram. In the upper left, you have your prototype, you might start with modeling or prototyping, some SPICE modeling. Left side is more verification/validation. At NI, our competency is on the right side,” where you work with engineers to automate testing. “NI helps engineers write a script that will help test this product. Then optimize those tests for speed and flexibility. The left side of the V is more interactive. We have changed what we are doing to be more interactive. We can help engineers get more flexible, get more input range. We can optimize for speed and flexibility in test, but get closer to the interactive test happening on the left side of the V, in design.”

Fig. 4: The Design V. Source: NI

NI says its sophistication in automating test can help the left side of the V. “You’ve set up all your instruments, you’ve configured all those instruments. We graphically, visually show you the results of those tests. You might pause the test and see what failed and we can give you the data behind that failure. It helps you. You might not jump to debug at that point, you might kick it back to design.”

NI’s automotive industry customers definitely “speak in the V,” says Driver. “We see a lot more design for test, and concurrent testing. However the engineer routes that board, does he have test points? We can determine that without having to create a whole new fixture. The trend is going there.”