Test Connections

In the Automatic Test Equipment (ATE) market, there's been a growing desire among users for a smaller-footprint, high-performance digital test subsystem. Recent advances in technology have made this desire a reality. David Manor, Geotest's vice president of Engineering recently wrote a paper for IEEE AUTOTESTCON 2010 that details how the PXI architecture can be used to implement a high-performance digital sub-system. He also explained some of the challenges that Geotest's developers faced and overcame when designing these systems.

Smaller can be better
According to Manor, the most important factors for users are the lower costs and smaller footprint associated with PXI-based test systems. These PXI test systems are easier to service and maintain, require less floor space, and can offer a more compact, shorter wiring interface to the unit under test.

The compact size of PXI also makes these instruments and subsystems more suitable for use in the field, and since they can potentially offer the same capabilities as depot testers, current applications can easily be re-hosted on these PXI-based field test systems. And because PXI is priced lower than other comparable modular platforms, acquisition and maintenance costs are lower.

high-performance PXI digital functional test subsystems

Fast and functional
Manor also states that improvements in Field-Programmable Gate Array (FPGA) technology have led to higher performance and increased customization of PXI instruments. Today's designers can put more circuitry into a single FPGA, requiring less board space and resulting in higher functional density for PXI instruments. Additionally, the technology allows the end user to change or update the product's functionality in the field simply by re-programming the FPGA.

On the software side, the need to maintain compatibility with existing legacy systems has resulted in the development of special software tools and converters. For customers looking to replace existing systems while retaining their investment in existing TPS', test program compatibility coupled with hardware compatibility represents a huge cost savings.

Putting it all together
The compact PXI form factor has presented some challenges for designers developing high performance digital instrumentation. As detailed below, these challenges required addressing several key issues in order to achieve all of the product's requirements and design goals.
Integrating pin electronics: Achieving the best driver/sensor performance and features with high channel count density is challenging. Because PXI can be implemented in a 3U or 6U form factor, Geotest needed to weigh the advantages associated with the larger real estate format against the marketability of a 3U product. For example, the space required to create on-board power supplies for a 3U implementation can affect the number of channels that can be implemented on a 3U versus 6U design. By adopting a 6U form factor and using highly integrated pin electronics Geotest was able to achieve designs with high channel counts without sacrificing features or performance.
Power requirements and power dissipation: High-performance pin electronics require creative and novel ways to manage power consumption and dissipation. According to Manor, one way to manage power dissipation is to use programmable power supplies for the positive and negative (VH and VL) voltage rails and control them through software, based on an application's specific drive/sense levels. By tightly managing the VH and VL power-supply voltages, you can minimize power dissipation, resulting in lower operating temperatures and increased reliability for the instrument.
Interface challenges: Providing a high-performance interface between the instrumentation and the Unit Under Test (UUT) has typically been a weak point for digital subsystems. With the availability of higher-performance connectors, you can use new methods for connecting to the UUT, which helps preserve signal integrity. An example is the VHDCI or SCIS3 connector, which accommodates off-the-shelf cable assemblies; provides impedance-controlled, twisted-pair cabling; occupies minimal board space; and includes a positive mating connection by means of jack screws.
Multiple-module synchronization: When an application requires more digital channels than one module can provide, you need to link together several modules to form a domain. The PXI standard has provisions for connecting modules using the trigger bus and local bus. You can use either bus for connecting timing signals between the modules, but the local bus is usually a better choice because it's not bound by segment size and the interconnecting lines have shorter stubs, offering a higher-performance transmission path for timing signals.

Geotest's new GX5960 digital subsystem incorporates all of these design features and offers the highest performance PXI digital test capability in the industry. Featuring per pin test capabilities, 1ns edge placement, multiple time sets, -10 to + 15 volts drive / sense capability, and per pin parametric measurement functionality, the GX5960 can be used for a wide range of applications from semiconductor to LRU / system test.
The GX5960 is available November 1st.

You can learn more about the GX5960, and search for similar solutions on the Geotest website.

You can read more about designing high performance digital subsystems here.
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