PXI for performance and low cost

03 January 2010

Due to the modularity of PXI, it is possible to quickly adapt to changing measurement requirements as the performance and speed of semiconductor devices continues to increase
Due to the modularity of PXI, it is possible to quickly adapt to changing measurement requirements as the performance and speed of semiconductor devices continues to increase

Adopting NI PXI for semiconductor validation has achieved performance improvements and cost savings, as Ray Morgan, Senior Product Engineer at ON Semiconductor, explains.

Increasing validation throughput for new semiconductor product introductions as well as legacy products with a low-cost solution that is accurate, precise, and easily upgradable with software and hardware is a challenge.

Replacing costly, standalone test equipment with a modular PXI-based platform that uses the latest processor technologies to achieve semiconductor validation at 10 times the speed and at a fraction of the space and price is the solution.

ON Semiconductor needed a low-cost solution to increase validation throughput for new product introductions. Along with the shortened evaluation cycle time and reduced cost, they wanted to develop an accurate and precise system that was easily upgradable with software and hardware for future use. The new system needed to handle the channel count of older high-speed and metal gate products, as well as newer high-speed voltage-level translators.

Advancements in semiconductor technology often resulted in costly standalone test equipment that quickly became obsolete for the applications. Because the next-generation test platforms had to be flexible enough to grow with technological advancements, the company needed to achieve upgradeable performance that could be easily integrated into the system with minimal cost.

A hidden cost with the previous platform was the time for test because the measurement throughput was often hindered by standalone instruments with varying processor speeds as well as complicated test set ups. Even though ON Semiconductor used a common software platform to automate the tests, the execution speed was limited by the slowest standalone instrument in the system.

In addition, instrumentation cost became an issue, because reducing the cost of test scrutinised every component of the test system. The investment in standalone instrumentation resulted in extra costs for redundant components that could be shared between instruments such as the instrument chassis, processor, and power supply. After conducting research, it was discovered that overpaying by three to five times was a possibility for standalone instruments versus comparable performance in a modular instrument platform.

The test platform addresses both AC and DC parametric testing of semiconductor devices, although in the past, the company performed AC parametric validation across 16 channels using multiple standalone high-bandwidth oscilloscopes. By adopting the PXI platform, they were able to spend $20,000 USD for one NI PXI-5154 1 GHz digitiser, two NI PXI-2547 8x1 multiplexers, and active probes, instead of invest more than $60,000 USD for four 1GHz oscilloscopes. This resulted in cost savings whilst maintaining measurement performance and integrity. In addition, the new platform performs tests 10 times faster than previous tests.

Two main variables were considered when using standalone instruments in an automated test system; the varying processor speeds between the instruments in the test system, and the speed of the bus used to connect all the instruments. Many systems are based on a GPIB interface, which is a common bus for communication. The modular approach, based on the PCI backplane, provides throughput increases for the current system and offers a method to achieve more improvements in the future by upgrading the PXI controller as new processors become available.

Migrating to PXI presented many challenges including connecting to the device under test. With four standalone oscilloscopes, it was possible to connect to and terminate all of the channels on a device under test simultaneously. A digitiser, like most standalone oscilloscopes, offers a 50Ω and a high-impedance (1MΩ) termination.

The challenge with a two-channel digitiser was that only two signals on the device under test are high impedance or 50Ω terminated at a time, leaving the other signals on the board un-terminated. The platform needed a connectivity solution that would allow high-bandwidth measurements with low-capacitive loading; characteristics typically associated with active probes, which are commonly offered with standalone oscilloscopes, but not readily available with digitisers.

By integrating high-impedance active probes along with probe power supplies into the system, all channels on the device under test were sampled and properly terminated without loading down the input or output. Most semiconductor products in the industry can be validated using this approach for AC timing characteristics. A modularised, PXI-based approach allowed for the quick adaption of the test platform to ever-changing measurement requirements as the industry performance and speed of semiconductor devices continues to increase.

In addition, a software interface to the instruments had to be created that is familiar and usable for test engineers and technicians. This challenge was met by enlisting the services of Systems Integration Plus Inc. (SPI Inc.), a National Instruments Alliance Partner and Certified LabVIEW Developer based in Scottsdale, Arizona. They branched subroutines, or LabVIEW VIs, into a friendly user interface for testing.

Most test and product engineers expect to be able to turn knobs and press buttons on their oscilloscope. The difference with a digitizer in a virtual instrumentation platform is that these knobs and buttons are now accessible with a single mouse click. Most PXI instrument vendors offer soft front panels that attempt to reproduce the hardware front panel found on standalone instruments. Instead, LabVIEW Vis was used which allowed for the customisation of the user interface and measurement routines. With this approach, the next-generation test platform eliminated the overhead, resulting in longer learning curves found in complex user interfaces of traditional standalone instruments.

The PXI platform set a new standard for semiconductor design validation and broke many of the paradigms and constraints of previous testing methodologies. Based on NI PXI technologies and the processing speed of a PC, it was possible to maintaine measurement and performance integrity while achieving a three times cost reduction and 10 times improvement in semiconductor validation time. It was also possible to reduce the test system footprint to a fraction of the space consumed by the former test solution. Because modular, PXI-based instruments now deliver higher performance that is also available with standalone instruments, PXI offers high-precision, accurate measurements for AC performance parameters that are commonly tested in semiconductor validation labs.

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