EDN was capable of tour the Si Labs engineering facility in Austin throughout Embedded world North America. The headquarters have been positioned a handy 15 minute stroll from the conference heart, making it a fairly pure option to discover. The tour primarily coated the analog and RF testing and validation processes with senior functions engineer Dan Nakoneczny and RF engineer Efrain Gaxiola-Sosa. Upon getting into, it was readily obvious that the power was properly stocked with high-spec check tools to conduct the vary of exams required. The lab managed to host massive home windows that permit within the Texas solar as a substitute of the standard check lab expertise—an “instrumentation cave” tucked away in a basement or some windowless-wing of a constructing. The unlucky aspect impact of this was a rise within the needed cooling required, inflicting a relentless hum of white noise.

Analog testing

Dan Nakoneczny started by displaying us the benches to check analog peripherals reminiscent of comparators, ADCs, voltage regulators, and oscillators. Typically, the workforce makes use of sockets to carry down the machine underneath check (DUT) which may very well be any of Silicon Labs’ SoCs the place the varied present, voltage, and timing measurements weren’t massively impacted by the socket and so they enable for one check setup between gadgets. “We are able to use the sockets for many of our exams however for different exams, like DC/DC converters, we now have to solder the elements right down to our boards,” defined Dan. The check bench included oscilloscopes, energy provides, operate turbines, and a binary counter, “with analog peripherals, you don’t have pins so that you’ll need to depend on simulations and have a extra oblique means of taking measurements of your system.”

For this lab particularly, the DUTs can vary from the standard gadgets in manufacturing to prototypes, “we’re constructing platform gadgets and numerous this IP will probably be used within the subsequent machine that may come out on the finish of the yr or in a few months, so the validation workforce is between the product engineering and design workforce looking for the small elements per million bugs, or points {that a} buyer would possibly discover throughout excessive quantity manufacturing ten years down the street. We are able to make modifications now earlier than it will get stamped into subsequent designs, the place we would need to do 10 totally different revisions,” stated Dan.

The automated check setup proven in Determine 1 features a decide and place robotic arm that makes use of laptop imaginative and prescient to seize and place DUTs within the socket earlier than urgent down the socket and locking the machine in place. All measurements go as much as the cloud to Silicon Labs’ database the place there are particular instruments used to visualise the information to, as an example, examine it with previous gadgets. 

Determine 1 Automated check setup that may be left for a weekend to check 20 to 50 elements.

RF validation

Receiver station

Efrain then guided us via the RF check stations scattered all through the lab and commenced on the receiver check setups that sat inside massive Faraday cages that offered as much as 135 dB of isolation to forestall any interference. The PCB offered in Determine 2 exhibits the Silicon Labs motherboards which are capable of obtain a number of daughter playing cards, “these are developed for every of our merchandise in order that the exact same infrastructure, connectivity, and adaptability in our lab can be utilized throughout a number of platforms. It’s slightly difficult to maintain them up to date on a regular basis, nevertheless it makes our life simpler,” stated Efrain. The RF exams have the distinctive problem of requiring soldered down DUTs so a correct check fixture is vital and utilizing the identical ones throughout the varied RF check stations and, as a lot as doable, throughout new manufacturing gadgets should be a problem. There are specialised motherboards that may go into the oven for temperature testing from -40^oC to 135^oC. “We’ve a bunch of switches and so we will check serially, however we can’t check in parallel as a result of our tools has a single channel for receiving info.” Efrain careworn that probably the most vital parameter from this check was receiver sensitivity; the higher the sensitivity, the extra vary the wi-fi sign had. These check setups are additionally largely automated and may be remotely logged into and managed exterior of the annual calibration required to make sure there are not any check errors resulting from drift.

Determine 2 Setup for the receiver testing with energy provide, a microwave swap system, sign generator, and PXI Categorical backplane chassis/modules.

In-band transmit station

The following cease was the check station for in-band transmissions, “we transmit in a number of protocols the place OFDM modulation is without doubt one of the most advanced. So we wish to be certain that we will transmit the excessive knowledge charges and that it’s ok for the receiver to really get this info.” Efrain reminded us that the standard of the transmit alerts relies upon largely on its error vector magnitude (EVM), inflicting this to be one of many extra vital parameters this station was meant to measure; nevertheless, the setup solely measured inside the ISM bands (e.g., 2.4 GHz and 5 GHz).

Determine 3 Check station for measuring in-band transmissions.

Transmitter out-of-band station

For out of band testing (Determine 4), check and validation engineers will check out the emissions on different bands together with mobile, radar, and many others. “Ideally you wish to transmit in your channel at a specific frequency alone, however you’re going to have harmonics that exist in frequencies which are a a number of of the basic frequency,” defined Efrain, “these can’t be greater than what the FCC permits.” He expressed how the nonlinear nature of fast-switching transistors are sometimes the wrongdoer of this EMI.

The out-of-band station is used for pre-compliance testing earlier than sending their half off to an accredited check lab for full compliance testing. “Our tools permits us to transmit and analyze a few of this knowledge (carried out emissions), so the output goes to the swap, the swap multiplexes the sign from the chip being examined, and this goes to the port of the spectrum analyzer the place we will do a number of operations,” Efrain said. An oscilloscope can be utilized within the place of the spectrum analyzer as properly to carry out different measurements. The facility provides inside the setup should be quiet and clear to take away any pointless inference from the check devices themselves. There are additionally battery emulators inside the setup since lots of Silicon Labs’ gadgets operate with batteries. 

Efrain continued, “We’re sending a sign with a given energy say, 1 mW or 0 dBm, the place we will go as much as 20 dBm. We wish to transmit on the highest energy doable the place one of many key figures is the output energy of our energy amplifiers; nevertheless, if we attain excessive output powers and we don’t cross FCC or ETSI necessities, we can’t promote.” On this station the ability of the basic is remoted and a notch filter is used to take away it and have a look at what’s showing on the harmonic frequencies. “If we depart the basic there, some power will leak and the measurement we carry out received’t be as correct,” defined Efrain. 

Determine 4 Check rack for carried out emissions testing. 

Radiated emissions testing

This check setup, naturally, won’t carry out radiated emissions testing. The Austin facility did home a small chamber for this designed by ETS-Lindgren with a robotic arm used to regulate the DUT for testing at numerous orientations. That is additionally used for pre-compliance testing. 

Receiver out-of-band emissions

At this level, we enter one more Faraday cage, this one a lot bigger to see how Silicon Labs exams how the receivers of their SoCs carry out with interference at totally different bands. “We’ve specialised tools to emulate an actual RF atmosphere so we check a specific set of alerts that might probably intervene with our DUT, and we wish to be certain that they don’t.” The setup proven in Determine 5, hosts numerous switches in order that the engineers can check in any respect the bands/channels of curiosity.  

Determine 5 Check station to measure how out-of-band interference may affect the receivers on the DUT.

Load-pull stations

The load-pull stations in Determine 6 have been a more recent check that the validation lab used to make it possible for the ability amplifiers (PA) have been delivering the utmost energy effectivity. Efrain defined how fabrication may barely modify the load habits of the DUT from being that extra preferrred ~50 ohms to one thing extra reactive or capacitive, “in these two stations we’re pulling the load that the PA goes to see. The change in impedance will imply that the ability we’re delivering just isn’t the identical and we have to establish what situations will make our energy amplifiers not behave correctly and convey that again to our design.” The purpose of the check was to construct a strong product that meet buyer expectations, “You’ll be able to say you promise a sure efficiency solely underneath preferrred situations, however are you able to management the output energy and do a suggestions loop to make it possible for what you say is going on on a regular basis?” 

Determine 6 Load-pull stations used to seek out the optimum load impedance on the chip pin for max energy switch and PA effectivity. 

Radio regression check system

The small shielded enclosures present in Determine 7 are a benchtop resolution for isolation (~80 dB) utilized by the PHY MAC workforce to conduct the battery of exams needed. There are 4 of those packing containers carrying check fixtures with 5 totally different DUTs, all linked to the Keithley’s S46 microwave swap system, configured as a 2:28 multiplexer (MUX). “The workforce does validation on the PHY and MAC degree to establish what we have to change or repair, and to ensure we don’t break something if we make modifications to firmware,” stated Efrain, “once you’re working with a number of radio protocols in a single {hardware} platform, it’s good to reconfigure your radio to assist these totally different protocols.” The check can also be used to emulate the fixes that Silicon Labs develops for purchasers that face points within the subject, “as soon as these points are mounted, they’ll come right here and hopefully they received’t break anything.” The regression stations run 24/7 with each day experiences on testing.

Determine 7 Radio regression testing with shielded enclosures to check PHY and MAC protocols of the varied radio fashions utilized in Silicon Labs SoCs.

Aalyia Shaukat, affiliate editor at EDN, has labored within the engineering publishing business for almost a decade with revealed works in EE journals and different commerce publications. She holds a BSEE from Rochester Institute of Know-how. 

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The publish An engineer’s playground: A tour of Silicon Labs’ labs appeared first on EDN.

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