For error analysis, it’s hip to be squared

I’m going to deviate from my normal coverage of modular instruments and alternative testing techniques, and focus on an associated design and test issue: error analysis.

Almost all analog designs require an error analysis. Components are not ideal; they all vary with regards to their specifications. Those variations add up in interesting ways.

I was deeply involved in error analysis when I was an analog engineer in the late 1970s and early 1980s.  Though Huey Lewis and the News hadn’t formed yet, that’s when I learned that it is hip to be squared.

What do I mean by that?

Basically, we choose components, each around a nominal value, to create a design. Lots of components. To statistically compute error bands of the entire design, I squared the possible error due to each component, summed them all up, and took the square root of the total. That would be error limit of the entire design. This is also known as RSS: Root of the Sum of the Squares. You can use RSS as a verb too, “I RSS’d the errors together.”

Why do I do that? Read the entire article here.

By Larry DJ

Top 6 modular instrument predictions for 2016

Last month I posted my Top 5 modular news stories of 2015. It was a mixture of technical trends and specific vendor news. The list made me think, “Could I have predicted these stories as the top news stories of 2015 at the beginning of 2015?” Possibly some, probably not others. Technical trends are easier to observe and predict than specific vendor moves. So, with that as a caveat, let me announce my top 6 modular instrument predictions for 2016.

You will find predictions about the test and measurement industry, growth of PXI and AXIe, RF & microwave opportunities, role of FPGAs, and vendor moves. To read my predictions, go here.

By Larry DJ

Are we privatizing test and measurement standards?



They have two things in common: They each manage standards for the test and measurement industry, and each of those standards is ruled by a private consortium.

It wasn’t always this way. When Hewlett Packard invented the 8-bit bus that would become known as GPIB (General Purpose Interface Bus), they were quick to bring the standardization effort to the IEEE where it was codified as IEEE-488.

Then, in 1987, something happened.

To read my entire column, go here.

By Larry DJ

AXIe nears the tipping point

If you’re a frequent reader of this column, you are probably familiar with AXIe. Positioned as the “big brother to PXI”, AXIe is a modular instrument standard similar to PXI in many respects, but utilizing a larger board format that allows higher power instruments and greater rack density. Since it relies chiefly on the same PCI Express fabric for data communication as PXI, it is nearly indistinguishable from PXI when viewed from the test system controller and is programmed similarly.

There’s a lot of news coming from AXIe these days. New vendors, higher speeds, new applications. Recently three vendors announced a major electronic warfare test win (photo above.)

Does this mean AXIe is near the “tipping point”, the point where critical mass is achieved, and the standard grows fueled by its own success?  If so, what would it mean for AXIe,…and PXI?

To find out, you’ll have to read my column, here.


By Larry DJ

Top 5 modular instrument news stories of 2015

Frequent readers know of this column’s particular focus on modular instruments, specifically PXI and AXIe. 2015 was another banner year for these standards as they continued to outgrow the test and measurement industry as a whole.

New products, new architectures, new vendors, and new applications continue to fuel the modular disruption in our industry. Since test and measurement dynamics change at a slower rate than those of the consumer industry, one can be forgiven for not recognizing the disruption occurring in our midst. A company does, however, so at its own risk. As 2015 winds to a close, I thought I’d choose the top 5 news events of the year that characterized the disruption we are now experiencing. Some are technically related, such as 5G wireless or FPGAs. Others cover surprise announcements from vendors such as Cobham, Keysight, or National Instruments.

To see the countdown of the top stories, click here.


By Larry DJ

Santa answers letters from anxious test engineers

I’m delighted to have Santa Claus “guest blog” for me this week.  Many test engineers have been writing to Santa, asking his advice on test systems, employee motivation, Internet of Things, on-time shipments, and relaxing after a large project.  To read Santa’s insightful and timely advice, go here.

By Larry DJ

Inside the Keysight 5G channel sounding system

Frequent readers of the Test Cafe blog know that I’ve added a recent focus on 5G characterization and test systems. Why? It’s simple. Test Cafe discusses instrument architectures, particularly modular instrument architectures, and 5G presents a key opportunity for modular instrumentation.

Due to 5G’s greater bandwidth and massive number of channels, I made an unequivocal prediction for vendors: if you don’t have a modular solution, you won’t be playing a significant role in 5G. Since that time, National Instruments and Keysight Technologies have introduced some exciting solutions in the 5G mmWave space, all based on modular instruments. Several weeks ago I described the internals of an NI system used by Nokia to create a 2×2 MIMO mmWave 5G prototype system, operating at 73 GHz. Now I’d like to take a look at the Keysight 5G channel sounding system, which combines elements of AXIe, PXI, and traditional instruments.

To read my analysis, go here.


By Larry DJ

AXIe specification gets an upgrade

Earlier this year, the AXIe Consortium added new capabilities to the AXIe Base Specification. If you are unfamiliar with AXIe, it is a modular instrument standard best described as the “big brother to PXI.” Like PXI, it hosts pluggable instrument and controller modules into a chassis, using PCIe (PCI Express) as a high-speed data fabric. However, the modules are larger than PXI and typically placed horizontally in a chassis. These larger modules allow power dissipation up to 200 watts/slot, suitable for high-speed data converters and digital test. You can read my recent AXIe tutorial here.

While AXIe consists of multiple standards numbered AXIe-n, where n represents a certain layer in the specification hierarchy, most references to AXIe assume AXIe-1, the Base Architecture specification. You can see the list of all specifications on the AXIe Consortium specification page.

So what did the AXIe Consortium change in the AXIe-1 specification? There are two substantial changes to the spec. First, it allowed expansion of the PCIe fabric from 4 lanes to 16 lanes, quadrupling data bandwidth. This capability is known as “Wide PCI Express.” Second, it made provisions for lower cost LAN-based modules.

You can read more details, and the significance of these enhancements, at my complete article here.


By Larry DJ

Keysight mobilizes for modular

A recent Friday morning found me at Keysight Technologies headquarters in Santa Rosa, California. Keysight, for those who somehow escaped this news, was the electronic test arm of Agilent Technologies, spun off as an independent company late last year. Agilent itself was a spin off of Hewlett-Packard Company in 1999.

My objective of the day was to catch up on the latest modular (AXIe and PXI) instrument happenings from Keysight, with a particular focus on 5G. I still plan to cover the Keysight 5G channel sounding system in a future column, but not today. A chance encounter with Keysight CEO Ron Nersesian changed the focus of this column to Keysight’s modular strategy.

My question to Ron was simply this: I’ve seen Keysight state that it’s goal is to eventually become the leader in modular instrumentation. Can you confirm? And if so, how do you plan to do so?

To read his response, read my entire column here.


By Larry DJ

Cobham leaps into AXIe

The modular instrument industry just became a bit more interesting. Cobham will be introducing a suite of modular products based on AXIe. Expect the introduction in early 2016.

For those of you without a scorecard, Cobham purchased Aeroflex in 2014. Aeroflex has been a major player in modular instrumentation for many years, focused on mil/aero and wireless test applications. In 2003, Aeroflex brought their first RF instruments to PXI.

Cobham’s adoption of AXIe has architectural and industry implications. Cobham exploited AXIe’s rack density advantage to deliver two 6 GHz transceivers in a single AXIe slot, equating to 10 per 4U chassis. This is approximately double the density state of the art PXI transceivers have obtained. Their wide PCIe backplane enables a nominal 16 GB/sec to each slot.  But will Cobham’s adoption of AXIe push it past the tipping point in application adoption?

To view photos and read the complete article, go here.

By Larry DJ