Tackling multiple domains

Sophisticated new multiple-domain instruments complement venerable standbys to help Prototype Engineering solve challenging design problems.

Rick Nelson -- Test & Measurement World, 10/1/2011 12:05:00 AM

Through patience and persistence, Ward Ramsdell (pictured) and Scott Clifford have acquired a bench full of both new and used test equipment for their start-up company. Photo by Robbie McClaran. See also: - Mixing domains - Videos of Ward Ramsdell working with the Tektronix MDO4000

HILLSBORO, OR—Take a look inside today’s electronic products and you’ll see traditional analog and digital circuit blocks, but you will also find high-speed serial I/O buses and, increasingly, RF circuitry. And when you are designing and testing such products, you cannot afford to treat the analog, digital, serial-bus, and RF domains in isolation. To speed up the design and debug process, you need to be able to correlate events in one domain with anomalies in another.

As electrical engineer and co-owner of Prototype Engineering, Ward Ramsdell leverages his expertise in the multiple domains to provide design-consulting services to serve a variety of customers: those with no in-house engineers, those whose in-house engineers are already over-tasked, and those whose in-house engineers lack expertise in a particular domain—often the RF domain. Said Ramsdell, “We provide turnkey product design—we work with customers who for whatever reason can’t complete their design themselves.”

Ramsdell cited several examples of designs he has completed: a consumer GPS receiver, an Ethernet-to-RF gateway, a USB software license dongle, a wireless speaker, and an I/O expansion board for the Arduino prototyping platform. He noted that his customers are generally savvy about their products: They know their market, they know what they want from a usability standpoint, and they can develop a coherent technical specification. But Ramsdell might be able to address some subtleties that the customer overlooked.

For example, Ramsdell said, the spec for the GPS device called for it to operate on AAA batteries. But consumers will plug in any type of battery that fits, so the product must tolerate the discharge properties of lithium, alkaline, and any other battery chemistries available on the market. Such tolerance for different battery chemistries isn’t explicitly called out in the customer spec, Ramsdell said, adding, “We have to read between the lines.”

To serve a diverse range of customers and support the design of a variety of products, Ramsdell maintains a lab equipped with everything from simulation software to mechanical-assembly equipment for building prototypes and machining test fixtures. A critical part of the lab is a bench full of test equipment ranging from brand-new, state-of-the-art instruments to used but fully serviceable models picked up at auction over the years.

And in many cases, Ramsdell said, used equipment is just fine. “I always say, the physics doesn’t change, and a good power supply is a good power supply.” Indeed, the lab is equipped with models still sporting the old Hewlett-Packard logo. Other venerable instruments he uses include discrete instruments such as signal generators, a VNA (vector network analyzer), multimeters, and power meters, as well as a rack of VXI gear. He said he would consider PXI if he were involved in high-volume manufacturing, but for his lab work, the VXI instruments are sufficient.

One service that Prototype Engineering offers that many consultants don’t is extensive automated characterization. “We do a lot of automated testing throughout the product’s expected range of temperature and voltage operation.” With respect to the GPS unit, he said, he ran thousands of power-on/power-off cycles and found that at low battery voltages and certain satellite orientations, the device would not shut off properly. It would have appeared to have powered-down to the consumer but would have continued to drain significant battery power. He traced the problem to a software bug that was easily fixed but could have been overlooked with a less-rigorous test.

“Automated testing is essential to cover all the corner cases to make sure the design is sound,” he said. As for high-volume manufacturing, Ramsdell said, “We would be happy to write automated test plans, but the ODMs [original design manufacturers] and CMs [contract manufacturers] often choose to do that to make use of their own test flows.” He noted that Prototype Engineering will provide support at the manufacturing stage, answering questions throughout the test-program-development phase and addressing yield issues during high-volume production.

Acquiring test equipment

Scott Clifford, co-owner of Prototype Engineering, gravitated to the engineering world after finding the insurance industry not to his liking. Photo by Robbie McClaran.

A key to putting together Prototype Engineering’s line-up of test equipment has been patience and persistence, said co-owner Scott Clifford, who handles sales and marketing for the company but who has acquired on-the-job engineering experience. He said that a consulting engineer or small engineering firm that suddenly needs a VNA could be in real trouble: Acquiring a VNA—even a used one—could be cost prohibitive. With a view toward starting Prototype Engineering, which began operations in 2005, Ramsdell and Clifford spent years seeking out bargains at year-end clearance sales, auctions, and used-equipment venues. “We had time to sit back and know where we were going and wait for the right pieces of equipment to present themselves so we could acquire them at a reasonable cost,” Clifford said, adding, “That allowed us to build a pretty well-rounded equipment base.”

Used equipment doesn’t always fill the bill, however. Although Prototype Engineering purchased a used VNA, Ramsdell said that state-of-the-art features such as autocalibration and fast measurement speeds make new models attractive, even though there have been no fundamental improvements in the Smith chart since it came out in 1939. And the oscilloscope, said Ramsdell, is one class of instrument that is evolving rapidly and for which it makes sense to acquire a new model that has mixed-signal or multiple-domain capability.

“Oscilloscopes are a place where people are still doing a lot of innovation,” Ramsdell said. “The logic analyzer seems to have gone the way of the dinosaur—a lot of people build the logic-analysis function either inside an FPGA or more-complex digital systems and access it using JTAG. But it is still nice to have 16 logic channels available on your oscilloscope to look at what’s happening” with the digital signals. He added, though, that he does occasionally break out a logic analyzer to debug system-level designs incorporating flash and RAM.

Of particular value, Ramsdell said, has been the new Tektronix MDO4000 mixed-domain oscilloscope, introduced August 30. As a beta-site customer who has been using the instrument for several months, Ramsdell said the MDO4000 is a valuable complement to his lab bench, minimizing the time from power-on to useful data. He added that the integration of domains eases visualization of system-level issues and allows him to focus on the product, not the test.

Specifically, the MDO4000 can capture time-correlated analog, digital, and RF signals across four analog, 16 digital, and one RF channel. The RF input frequency range extends up to 6 GHz and provides a capture bandwidth of 1 GHz or better at all center frequencies. The instrument can display up to four decoded buses—serial, parallel, or a combination of both—at one time. The time correlation between domains enables engineers to make accurate timing measurements to understand delays and latencies between command and control events in their design and changes in the RF spectrum.

Correlation is key

The key word with respect to the MDO4000 is correlation, Ramsdell said. “You are correlating operation of one part of the system to operation of another part of the system. And that is something that has not been done well before. It is something you have been able to do only with a whole lot of effort on your part.” And that effort, he said, must be repeated to address every specific test scenario you face. “The reason the MDO is attractive,” he said, “is that it addresses the general case of something that is transmitting a radio signal or otherwise exhibiting electrical activity, which is everything under the sun.”

He likens an engineer making tests without an instrument such as the MDO4000 to a doctor trying to make a diagnosis by taking x-rays of an elbow and wrist—the hyperfocus on the wrist and elbow misses the fractured forearm between the two. The MDO4000 makes the hyperfocus approach unnecessary, he said. “Being able to grab a broader swath of information and dig into it quickly and efficiently is really what speeds up the process.” The alternative of devising many different test scenarios to each of many possible causes for a single problem is just a time sink, he said. For each scenario that doesn’t pinpoint the problem, he added, “You are not really learning anything, you are not gaining insight, you are just spinning your wheels.”

FIGURE 1. By moving the MDO4000’s Spectrum Time window throughout the time-domain acquisition, designers can see the RF spectrum for any point in their acquisition while simultaneously viewing time-domain information. Shown here is a VCO output spectrum (bottom) captured after the PLL voltage settles out. Sliding the Spectrum Time window (orange bar in the time-domain display; indicated by arrow) to the left would let a designer see how the frequency changes after assertion of the VCO enable signal. Courtesy of Tektronix.

To help designers avoid spinning their wheels, the MDO4000 allows designers to see the RF spectrum of a signal at any point in time within a long acquisition to see how the spectrum changes over time or with device state. By moving the instrument’s Spectrum Time window throughout the time-domain acquisition, designers can see the RF spectrum for any point in their acquisition while simultaneously seeing their analog, digital, and decoded buses at the same point in time. For example, users can use the instrument to view the spectrum as a VCO/PLL turns on (Figure 1) or measure the transition characteristics of a frequency-hopping RF signal. In addition, they can find the source of intermittent, device-state-dependent EMI (electromagnetic interference) noise.

EMI issues present challenges for virtually every electronic product, whether it’s an intentional radiator or not. Said Ramsdell, “Spurious emissions from your circuit are 90% of the time not even related to the radio—they are related to some transient condition that exists elsewhere in the product. The system may be transitioning into some weird mode, generating a blip in the radio spectrum that causes you to fail” your EMI-certification tests. The MDO4000’s ability to relate RF spectrum and time-domain events, he said, can help users quickly pinpoint problems.

Prototype Engineering does not have a large anechoic chamber but works in conjunction with companies that do, such as Northwest EMC, to help customers achieve compliance. For an intentional radiator, he said, the certification process can cost the customer about $10,000 and take one month, including one week in the chamber plus a big paperwork exercise.

Growing the company

Ramsdell and Clifford are looking to leverage their collection of equipment and combined expertise to expand Prototype Engineering, providing consulting engineering services and completing their own designs. Ramsdell brings to the company his electrical engineering education at Rochester Institute of Technology, where he also taught graduate and undergraduate lab courses, plus experience at companies large and small, including at Nortel, TriQuint Semiconductor (where he met Clifford), and Beaverton-based start-up Avnera.

Ramsdell said he always knew he wanted to be an engineer and acquired his first oscilloscope at age 11. He said that when he reached college in the mid-’90s, many students were focusing on digital technology, but he chose to study RF, in part because the discipline was perceived as difficult and in part because, with cellphones proliferating, he thought wireless technology would take off.

Clifford came to Prototype Engineering via a different path, having studied finance and management at the University of Oregon and working for a couple of years at an insurance company. Finding that work not to his liking, he moved to the high-tech field and gained experience in both R&D and manufacturing.

The company’s next step might be to hire a firmware specialist to complement the skills that Ramsdell and Clifford already bring to the firm. Ramsdell added that the direction the company takes would be affected by the character of the people brought on board. “We want to pride ourselves on our ability to build a company that fits the abilities of our employees,” he said. He added that one former colleague accused him of wanting to start a “lifestyle” company. His response: “We want to build a company where people are comfortable, enjoy what they are doing, and feel valued. If you want to call that a ‘lifestyle’ company, great.” T&MW

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Rick Nelson was editorial director of T&MW when he wrote this article.

Mixing domains Engineers are increasingly working in both the time and frequency domains as the products they are designing increasingly incorporate wireless functionality. To help them out, Tektronix has introduced what it calls an MDO (mixed-domain oscilloscope), which combines the functionalities of an oscilloscope and a spectrum analyzer in a single instrument. The combination saves bench space, obviously, but the key benefit is that the combined instrument lets engineers capture time-correlated analog, digital, and RF signals. Speaking at a prelaunch briefing at the International Microwave Symposium in June, Ward Ramsdell, an electrical engineer and principal at Prototype Engineering, discussed his application of the new instrument to academic, RF semiconductor, mixed-signal semiconductor, and consumer-electronics product-development efforts. Ramsdell provided specific demonstrations of the MDO4000, including exploration of digital RF modulation in an academic setting, mixed-domain analysis of a cellular power amplifier, the analysis and debug of a wireless audio IC, and debug of a 900-MHz low-data-rate radio. Also speaking at the prelaunch briefing in June, Roy Siegel, GM of oscilloscopes at Tektronix, said that more than 60% of oscilloscope users also use a spectrum analyzer to troubleshoot embedded system designs with integrated wireless functionality, requiring them to work in both the time and frequency domain. Putting the spectrum analyzer within the oscilloscope, he said, supports cross correlation to enable engineers to determine what time-domain events cause frequency-domain anomalies. Siegel said the integrated instrument can help save days or even weeks of debug time.—Rick Nelson The Tektronix Website includes the following videos of Ward Ramsdell working with the MDO4000: Ward Ramsdell reviews of MDO4000 series Ward Ramsdell investigates the turn-on characteristics of a 2.4-GHz power amplifier Ward Ramsdell debugs a low-power radio Ward Ramsdell validates a wireless audio device