The Automated Test Blog

As recently discussed in a post by Rick Nelson of Test and Measurement World magazine, the Semiconductor Test Consortium (STC) has begun work on defining a Portable Test Instrument Module (PTIM) - a standard plug-in module for performing ancillary measurements on existing semiconductor ATE.  My colleague, Luke Schreier, delivered a presentation at the last STC global meeting that was very well-received which proposed PXI as a suitable specification to build from.   The business case is very compelling - traditional ATE architectures are built to accommodate the densest and highest speed test pins possible - 1 kilowatt of power per board is not uncommon.  This is necessary for the high speed digital electronics needed to test the latest processors, for instance.  When you need to add some audio or RF measurements into the system, however, the infrastructure can be overkill.  Moreover, to fully integrate an instrument into a tester requires expertise of the ATE vendor, so to make these measurements, the vendor may be required to invest significantly in development of measuement functionality already available on the open market, just in other form factors.

It is interesting to me that the semiconductor test industry is recognizing some of the features we designed into the original PXI specification.  In fact, one of the slides we used to use in the early days of PXI showed a set of rack and stack instruments on one side and a “big iron” semiconductor tester on the other, with PXI right in the middle.  The point was that PXI borrowedconcepts from both of these markets - the measurement quality from box instruments, and the card modular form factor and integrated timing and synchronization from semiconductor ATE.  It looks like after 10 years, its finally come full circle.

I was recently invited to give a talk at the VLSI Test Symposium titled “Migration of PXI Instruments into Semiconductor Test“. The session focused on emerging trends in semiconductor ATE and on work that is currently going on in both vendors consortia, to migrate PXI into semiconductor test applications. The presentation covered the key challenges currently facing engineers that are validating and testing increasingly complex devices such as SoCs and SiPs. As I previously blogged, Protocol Aware ATE is a new technique for testing these complex devices at a system level. In the presentation, I also covered existing work to build semiconductor ATE based on PXI, including examples of augmenting existing ATE, creating testers with a PXI measurement core, and work by the Semiconductor Test Consortium on a Portable Test Instrument Module, or PTIM. The PTIM initiative is designed to provide a way to add ancillary measurement capability to existing ATE platforms. The STC has been evaluating various options and has the desire to standardize PTIM on an exiting industry standard. PXI has been proposed as the PTIM platform and is currently being discussed at the Global STC Conference this week in San Diego. This proposal will enable ATE customers and vendors to leverage the large commercial investment in PXI and extend ATE capability by using the 1500 existing PXI modules currently available.

OK, time for the last of my 5 trends in test for 2008:

Emulation-Based ATE That Improves System-on-a-Chip and System-in-a-Package Testing

As semiconductor devices become more complex, the process of testing each part completely with a traditional vector-based methodology is increasingly difficult. Complex systems-on-a-chip(SoCs) and systems-in-a-package (SiPs) require a system-level functional test more closely related to testing components placed on a printed circuit board than a typical chip test, but they still require the high speeds demanded in production test for the semiconductor industry. The strategy of testing a device by emulating actual real-world signals provides a better method of functional test for these types of high-speed systems. This emulation-based ATE, or also termed “Protocol-Aware ATE” during last year’s International Test Conference, combines FPGA-based hardware to emulate the rest of the system in real-time with the pin electronics found in traditional ATE. This lowers the total cost of test through better use-case coverage and improves the user’s ability to debug failures. I explained this idea in more detail in a recent blog post. In 2008, I expect more vendors to incorporate elements of emulation-based tests into traditional tester architectures and for more users to incoproate platforms currently used in functional test, such as PXI, into chip validation and test applications.

As I stated in my last blog, I’m planning to discuss one trend per blog entry over the next few weeks. The second trend in Test and Measurement is:

Growth of Software-Defined Instrumentation

One issue facing test engineers is that test instrumentation is not updated as rapidly as the devices being tested. The functionality of these complex devices is being defined by the software embedded in them, such as the Apple iPhone, which gives design engineers the ability to add features faster than ever before. This is increasingly challenging for many test engineers because most stand-alone instruments often lack the measurement capabilities of the most recent standards due to the fixed user interface and firmware that must be developed and embedded in them.
Thus, test engineers are turning to a software-defined approach to instrumentation which gives them the ability to quickly customize their measurement algorithms and user interfaces to meet specific application needs and integrate testing directly into the design process, further reducing development time. PXI is the example of a widely used software-defined instrumentation standard for building modular, reconfigurable high-performance automated test systems.

Kiran Unni, Frost & Sullivan Measurement & Instrumentation research manager, recently confirmed that PXI is influencing this trend when she stated, “The adoption of tools such as PXI is an indicator that companies recognize the benefits of moving toward software-defined instruments. The savings being realized in capital equipment, system development and improvements in system efficiency all contribute to reducing the per-unit cost of test, directly influencing the bottom line.”

I recently presented at a group called the Semiconductor Test Consortium, or STC. There were two subjects of the talk – learnings from PXI and other industry standards and emerging trends in SOC (System On a Chip) and SIP (System In a Package) functional testing. The latter has been the subject of some interesting discussion of late in the semiconductor test industry.

The challenge that many chip designers face is that the devices are increasing in complexity at a rate that exceeds the advances in testing technology. The result is that the cost to manufacturer complex semiconductor devices is decreasing faster than the cost to test them. In validation, the issue is not only test cost, but overall test time, which can impact the time to validate new silicon and, ultimately, time to market.

As devices begin to resemble complete systems, a higher level test methodology is called for to both reduce the tester’s complexity, as well as provide a tighter link back to the system level design tools. An engineer at Broadcom recently coined the term “Protocol Aware ATE” to describe this need and at the International Test Conference (ITC) this year, there was a panel discussion on this trend. The idea is to create a test system that can perform functional testing of a device by emulating the device in situ, or in its intended surroundings. This requires the capability to model the other components of the system and to interact with the device in real time.

This is similar in many was to functional testing that is already routinely done at the board and system levels. For some devices, this is just stimulus-response type testing performed at the end of the manufacturing process. When real-time response is needed, this is very similar to a technique called Hardware in the Loop, or HIL, used extensively in automotive and aerospace validation testing. For chip testing, the real time requirements are often more stringent. A technology that has promise to meet many of these requirements is the Field Programmable Gate Array (FGPA), also noted as an ideal architecture in the Broadcom paper. A programmable FPGA placed in the tester close to the device under test, can be used to emulate the system and test the device in situ. The FPGA also holds promise as a target that can run system models directly from system level design tools to bring design and test closer together.

I came across an interesting blog post by Richard A. Quinnell, Technical Editor — Test & Measurement World.  In his blog, he made the following statement, “With just about everything going wireless, I’ve started wondering when PXI will join the parade.”  I felt a response by our PXI Marketing Group Manager, Richard McDonell would be appropriate.  

Guest Blogger: Richard McDonell – PXI Group Manager

Every day I learn about another common device that has gone wireless…from cell phones to game controllers to PCs and laptops.  In each of these cases, the wireless interface is replacing a previously wired solution providing increased range, improved flexibility, and added user-convenience.  These are great benefits, so why hasn’t PXI gone wireless?  Well, in many ways it already has.  PXI is already being used to design and test thousands of wireless devices and you can use a wireless (802.11) LAN interface to transfer data to other systems or back to a network location.  Wireless LAN interfaces can also be used for controlling your PXI systems remotely.   

So why not decouple each PXI module from a wired PXI bus and connect them using a wireless protocol?  Technically, there is no reason why you couldn’t do this.  The real question is do you really want to?  Unfortunately, the convenience of a wireless interface doesn’t come without tradeoffs in performance, setup ease-of-use, and cost.  The core benefits of PXI come from the shared card cage architecture, the high bandwidth and low latency PCI and PCI Express bus, and integrated timing and synchronization (I suppose this could also count as “wireless” since PXI eliminates the need for most external trigger and synchronization cables).  Separating each PXI module into its own separate sub-system via WiFi would dilute the benefits of PXI and significantly decrease the performance (due to increased bus latency), cost (due to dedicated fans, power supplies, and boxes per device), and synchronized measurement accuracy (due to a lack of triggering) that PXI offers in its current state compared to traditional standalone instrumentation.  You would however retain the user-defined software aspects of PXI in such a configuration which is a key component of PXI’s measurement flexibility and reuse.   

Thus, I do not feel wireless PXI in the form of discrete PXI devices connected via wireless interface is worth the effort.  However, I would agree PXI is the ideal platform for designing and testing wireless devices and that it enables higher performance, lower cost, and improved flexibility in most test and control applications today.

I just read the latest 2007 Test and Measurement Salary Survey. One of the questions that really peaked my interest was on the topic of what technologies are engineers being required to learn. The number one test platform listed was PXI (20% of readers listed it), with PXI Express, an extension to PXI, a close second. This is just another example of the increasing industry adoption of PXI. Most of the other technologies engineers are being asked to learn are communication protocols - Firewire, WLAN, and WiMAX were all high in the ranking.

One the biggest signs of success factors of PXI has been the increased adoption by major test and measurement vendors. Even though at times they have been hesitant to wholeheartedly support the PXI standard, Agilent, has several product lines in PXI:

•  A line of PXI-based high performance signal generators (N6030A)
• PXI digitizer modules, from their acquisition of Acqiris
• PXI Optical test instruments, form their acquisition of PXIT

Last week, Agilent released new PXI modules in their optical test product line. Their press release notes that the modules offer their customers “a smaller, faster, more cost-effective solution” - precisely the primary benefits of the PXI platform.

I’d like to clarify the difference between these two terms as I have found that there is very often confusion between them. The distinction is entirely in the software model and the programmability of software-based analysis by the instrument user. A Virtual Instrument’s primary programming model is to present raw data to the user for customized measurements. A Traditional Instrument’s primary programming model is to present vendor-defined measurements to the user.

What about Standalone Instruments versus Modular Instruments? This is a question of form-factor, not software, and is therefore entirely orthogonal to whether the instrument is virtual or traditional. A standalone instrument can indeed be used as a virtual instrument. An example is a standalone oscilloscope that is automated to create custom measurements in software. Similarly, it is possible for a modular instrument to present only a traditional use model to the user; VXI instruments, for example, were most often vendor-defined instrument repackaged in a modular form factor.

While the definition of virtual instruments and modular instruments is orthogonal, it is true that many modular instrument standards lend themselves to building virtual instrumentation systems. In order to effectively perform user-defined analysis on a signal, the user must have access to the raw data from the instrument’s acquisition. For high-speed measurements, this requires transferring many megabytes of data from the instrument to a processor to be analyzed in software. High-speed interface buses such as PCI Express, which can transfer data at up to 4 Gigabytes/s, are well-suited to this application. Instrumentation standards such as PXI combine high-speed buses and upgradeable PC-based processors, making it an ideal platform for virtual instrumentation systems.

PXI is celebrating its 10 year anniversary in 2007. Richard Quinnell at Test and Measurement World recently wrote about PXI’s anniversary, highlighting the compatibility it has achieved during this time. For me, its been remarkable to see the growth and changes in this marketplace over the past 10 years, especially all the times that PXI vendors achieved “the impossible”. Here are a few of my favorites:

• 1999 - 50 members and over 200 products. The first few years of the standard saw a rapid adoption by vendors and the release of a lot of products. Grow exceeded expectations in every dimension.
• 2002-PXI’s entry ito RF. Prior to the release of products by National Instruments and Aeroflex, certain vendors had been outspoken that “you could never do RF in PXI”. Last year, Phase Matrix announced that they are taking PXI all the way up to 26.5 GHz!
• 2003 - PXI systems shipments exceed VXI. By 2006, PXI vendors shipped over 10,000 systems per year - 3 times larger than VXI at its peak. Naysayers claimed modular systems would never be mainstream.
• 2004- A 512 Cross-Point Switch. With the release of the PXI-2532, National Instuments put to rest those that claimed the Achilles heal of PXI was switch density.
• 2005-PXI Express. The PXI Systems Alliance did a remarkable job incorporating new technology to achieve a 45-fold increase in bandwidth while preserving backward compatibility. Those that claimed PCI Express would break compatibility become suddenly quiet.
• 2007 - Agilent joins the PXISA. Agilent Technolgies joined other big name vendors such as Advantest, Aeroflex, Keithley, National Instruments, Rohde & Schwarz, and Teradyne. So much for not having any big name companies in PXI!