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Instrumentation bus eyes Express lane

Posted: 03 Oct 2005 ?? ?Print Version ?Bookmark and Share

Keywords:express? pxi systems alliance? pxi?

The PXI Systems Alliance detailed a standard last week for hardware based on PCI extensions for instrumentation, or PXI. By this time next year, vendors in this fast-growing market expect to ship test and measurement modules that take advantage of the improved accuracy and much higher bandwidth supported by the PXI Express standard.

Revenue increased by 40 percent last year in the PXI-based hardware market, according to market research firm Frost & Sullivan. By leveraging PC technology and standards, and largely using industry-standard components, PXI vendors have been able to offer flexible, multifunction instrumentation solutions.usually controlled by the LabView graphical programming tools.that often sell for much less than rack mounted instruments.

PXI Express is based on the PCI Express protocol now used in desktop PCs. In 2004 and into the first half of this year, the PCI Industrial Computer Manufacturers Group, which controls the CompactPCI standard used in industrial and telecom applications, set about adapting PCI Express for industrial applications.

Members of the PXI Systems Alliance took part in the effort to create the CompactPCI Express specification, then spent the last six months developing the additional features required for instrumentation and test, said Mark Wetzel, chairman of the PXI alliance technical committee and an engineer at National Instruments Corp. Alliance members have also developed a hybrid connector that accepts either PXI or PXI Express modules.

Tim Dehne, senior vice president of research and development at National Instruments here, said that the PXI Express standard will support future growth in high-performance instrumentation, RF test, machine vision and surveillance, "and markets that we haven't thought of yet."

Bandwidth, speed boost

At 6GB, the bandwidth from the host controller to the backplane of PXI Express is about 45 times greater than in the PXI standard, which was limited to 132 Mbytes of total bandwidth. Also, PXI Express moves to 100MHz differential signaling, rather than the 10-MHz single-ended signals of the PXI standard.

That will increase the speed at which signals are sent from one board to another within a chassis, giving PXI Express-based instruments picosecond-level triggering and much-improved synchronization, according to Wetzel.

The PXI-based boards are used within a ruggedized chassis that usually includes a PC module as the controller. The higher bandwidth between the host and the boards could make it possible to save on system memory costs, keeping more of the memory on the host controller board rather than on the individual instrument cards. Some higher-performance instruments have $500 to $2,000 worth of memory on each card, Dehne of National Instruments said, and it may be possible for some cards to have less memory on board and to rely on the host memory instead.

Wetzel said costs will be shaved by removing a phase-locked loop (PLL) component used on many PXI instruments that have FPGAs on board. The 100-MHz differential signaling is fast enough to communicate directly with FPGAs, while the 10-MHz PXI signals required a PLL to link to FPGAs, which normally do not operate at such slow frequencies. The reduced memory footprints and the ability to remove the PLL raises the possibility that PXI Express instruments could have a lower bill of materials and be higher-performing to boot, Wetzel said.

Also, the PXI Express standard does a much better job of ensuring that each board within a chassis receives a guaranteed minimum of bandwidth. Gutterman said eight cards could each receive 250MB of bandwidth, or a maximum of 2GB for a single card.

With the PXI standard, a vision card, for example, easily could suck up all of the available 132MB of total bandwidth, starving the other cards within the chassis, said Darcy Dement, a product-marketing manager at National Instruments. That is unlikely to occur with PXI Express systems, she added.

A Frost and Sullivan analyst who goes by the name of Karthik. R said that his only complaint with the PXI Express standard is that it took too long to evolve, coming several years after Intel Corp. first developed the PCI Express standard. With the imminent approval of the standard, Karthik. R said, "My strong feeling is that PXI Express will drive the PXI market to further growth.

Besides National Instruments, companies such as Aeroflex Test Solutions, Geotest, Racal Instruments and several other midsize corporations are climbing on the PXI bandwagon, the Frost and Sullivan analyst said.

Market impact

The higher bandwidth will "affect quite a few markets, and give the PXI vendors the ability to support higher-channel-count acquisition boards, for example," he said.

The PXI Express standard will be particularly useful in measuring wireless systems that have much higher signal bandwidth, said Bill Burrows, director of product marketing at Aeroflex (Wichita, Kan.). Now that the WiMax (IEEE 802.16e) standard is being considered for fourth-generation cellular networks, wireless-system companies need measurement systems that can earmark channels for multiple destinations, thus sharply reducing the time needed to make measurements.

"It may take about two years before the market sees a lot of measurement systems based on PXI Express. But it will extend the life of PXI for the next 10 years at least," said Burrows, who came to Aeroflex when it acquired the wireless-instrumentation operations of Marconi Corp.

PXI Express could have a major impact on machine vision, medical imaging and surveillance systems, giving them the ability to divide the 6GB of bandwidth into eight high-resolution channels, said Abhijit Athavale, a marketing manager at Xilinx Inc.'s connectivity solutions division. "If you look at surveillance systems now, the images are too grainy. The resolution could easily double, and that could help us catch criminals," Athavale said.

- David Lammers

EE Times

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