PXI breathes new life into legacy test systems
01 May 2022
Figure 1. TS-9XXe-5G multi-port architecture
Deploying test systems to the factory floor is never the endgame for a test engineer; they always face the challenge of enhancing functionality when test requirements change, as well as the need to keep existing test systems
operational when instrumentation or switching face end-of-life & obsolescence.
This article was originally featured in EPDT's 2022 PXI for T&M supplement in the May 2022 issue of EPDT magazine [read the digital issue]. And sign up to receive your own copy each month.
As Jon Semancik, Director of Marketing at T&M firm for military, aerospace & manufacturing organisations, Marvin Test Solutions tells us here, one proven method to mitigate the impact when implementing these test system changes is to adopt a modular open systems approach (MOSA), featuring PXI-based solutions…
Adopting a MOSA philosophy for test system design offers numerous advantages, from both a technical and business perspective, such as delivering systems that are more affordable, highly adaptable, better positioned to incorporate new functionality and well suited to address the inevitable sustainment issues that will arise. PXI-based systems were at the forefront of MOSA designs long before the term was coined, and continue to provide solutions to address a broad range of functional test and data acquisition applications. This approach provides a viable, cost effective alternative for mid-life upgrades of proprietary ‘big iron’ and classic ‘rack-and-stack’ test system implementations, ranging from incremental performance improvements to implementing entirely new measurement capabilities.
A perfect example of technological change that is driving the need to update existing proprietary ‘big iron’ semiconductor test systems with entirely new measurement capabilities can be seen in the development and adoption of 5G communications. Beamforming integrated circuits (ICs) provide the ability to generate and steer radio (RF) energy; current systems operate between 24.25 GHz and 52.6 GHz, with future requirements identified for frequencies between 64 GHz and 86 GHz. Existing semiconductor test systems do not provide test capabilities at these higher frequencies, presenting a significant challenge for manufacturers as they race to release new devices – especially if existing suppliers do not feel the same urgency to upgrade support for these types of tests.
PXI-based test systems are the ideal solution, whether to address incremental upgrades, or for a complete turnkey system. Vector network analysers (VNAs) are at the heart of any high performance mmWave test system; these specialised RF analysers provide both amplitude and phase measurements to deliver results that are far superior to scalar network analysers (SNAs), which only return the amplitude properties of the measured signal. Phase measurements are essential when testing mmWave devices, as digital phase adjustments provide the ability to steer the RF energy.
Figure 2. PXI-based TS-900e-5G mmWave semiconductor device test system
Accurate and repeatable phase and amplitude measurement across the entire band of interest is another critical characteristic of the VNA. Some VNAs may be capable of analysing signals across their entire operating band, 100 kHz to 40 GHz for example, but there may be dead bands or frequencies where the response is below levels that are acceptable for evaluating the device-under-test (DUT). The Keysight M980aX proved to be the ideal VNA solution for MTS’ TS-9XXe-5G series of mmWave semiconductor device test systems,delivering modularity, speed and accuracy in a multi-port instrument that shares the same measurement science as PNA-X instruments commonly used in the laboratory, with no dead bands across the operating spectrum.
Test speed and system throughput are essential for production mmWave test systems, and this places additional demands on the RF measurement subsystem. Most beamforming devices are multi-port ICs and a common four-port device would incorporate one RF feed and four RF input/output antenna ports; therefore, five VNA channels are required. The density of these devices continues to increase, and as a result, the architecture of the test system will greatly impact overall throughput and scalability. For example, some manufacturers have already transitioned to higher density beamformer ICs with two RF feeds and eight RF input/output antenna ports. These evolving needs clearly highlight the advantages of the PXI MOSA approach, allowing test systems to easily adapt to changing needs through the installation of additional VNA instruments, utilising the chassis’ spare slots.
Some test architectures will reduce the overall number of independent VNA instrumentation ports by implementing a multiplexed switch topology on the front end of a rack-and-stack instrument. This approach will certainly reduce the number of required VNA ports, and their associated cost, but it will also impact reliability, measurement uncertainty and test times. Mechanical microwave relays tend to be the technology of choice when implementing these RF multiplexers, with each path having slightly different insertion loss and VSWR (voltage standing wave ratio) characteristics, and a finite lifecycle, with performance that degrades non-linearly over time, which must be addressed through careful calibration processes. Additionally, relay actuation and settling times greatly increase test times.
PXI-based solutions can easily deliver true multi-port, parallel test architectures that allocate an independent VNA port for each port on the beamformer IC by incorporating additional PXI VNA instrumentation; this approach delivers considerable advantages in system throughput and reliability. Parallel, multi-site architectures not only significantly reduce test times, but also eliminate the need for external microwave switching, and the issues associated with measurement uncertainty and reliability. These levels of performance have quickly become the industry benchmark, highlighting the clear advantages of the PXI-based parallel multi-port/multi-site architecture (Figure 1).
Figure 3. MTEK semiconductor test capability enhancements
The PXI-based TS-900e-5G (Figure 2) is a turnkey 5G mmWave semiconductor device test system incorporating commercial off-the-shelf (COTS) instrumentation with gap-free VNA RF (up to 53 GHz) performance, dynamic digital I/O with parametric measurement unit (PMU) per pin, and device power supplies with source/measure (SMU) capabilities.
The PXI platform also provides the cleanest approach to implement incremental upgrades to existing test systems, such as channel expansion, higher dynamic digital vector rates or additional device power supply channels, without the associated capital investment of complete system replacement. The MTEK (Marvin Test Expansion Kit) Subsystem (Figure 3) provides a straightforward approach to implement these upgrades, a need that is common across multiple industries from semiconductor to military & aerospace to industrial, where modularity and the use of COTS technology is highly valued.
One such example involved adding advanced dynamic digital capabilities, with increased vector rates and deeper on-board memory, to support new product releases on an existing legacy semiconductor test system. The MTS GX5296 dynamic digital I/O card with per channel programmable logic levels and parametric measurement units (PMUs) was selected, but PXI’s modularity and open system architecture enables adding hardware from other suppliers as needed to meet new and emerging test requirements. MTEK allows customers to enhance system capabilities by configuring a subsystem with exactly the resources needed: RF, digital, analogue, switching or power.
PXI-based test systems unquestionably deliver the measurement performance needed to address the most challenging test applications in the industry, but they also incorporate inherent advantages over other approaches including affordability, adaptability, flexibility and an extensive ecosystem of suppliers offering a wide range of solutions. Whether designing a test system from scratch, or enhancing capabilities to extend the usable life of existing systems, PXI continues to be the test solution of choice.
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