Addressing Legacy Test System Replacement

Author : Mike Dewey, Director of Marketing, Marvin Test Solutions

12 May 2017

Companies and government entities continually struggle with ways to extend the life of their test equipment and systems. Military contracts require test support for the life of the program which can be a 15 to 20 year requirement. Similarly, high value, mission-critical electronic products which rely upon functional test also exhibit extended lifecycles.

This article originally appeared in the July 2017 issue of Electronic Product Design & Test; to view the digital editionclick here – and to register to receive your own printed copyclick here.

As shown in Figure 1, it is not unusual for product support for military programs and the associated test equipment to extend beyond a 20 year period, presenting a significant challenge to test engineers and management when dealing with maintenance and support for the associated legacy test systems. 

Many of these legacy functional test systems were supplied by commercial vendors including Teradyne, GenRad, and Schlumberger. Based on proprietary hardware and software architectures, these systems were used for functional test and verification of high value, mission-critical products including: 

  • Board and box level avionics
  • Airborne electronics
  • Communications and satellite subsystems
All of these legacy test systems have been out of production for over 10 years, with maintenance and repair support by the OEM unavailable. However, many of the products originally tested on these platforms are still in use and need to be maintained. Consequently, companies and government entities that design, build and/or maintain these test systems face the question of whether to extend the lifespan of these systems via selective component replacement / upgrades or pursue a system replacement strategy.

Test System Requirements

Test engineers continually evaluate the “maintain or replace” strategy and need to assess the total cost of replacement. And to accurately assemble replacement costs for a test system, one needs to understand the capabilities of the existing legacy ATE platform and associated test programs. The described legacy test systems were strong test platforms and when these systems were developed and deployed, the goal was to provide a test platform that could address many test strategies (in-circuit or functional, among others). However, for most applications and particularly for mil-aero related products, these test systems employed functional test methods almost exclusively. Consequently, the capabilities and requirements associated with replacement solutions are primarily focused on supporting digital and analog functional test capabilities which need to include the following attributes and capabilities:

  • A high-performance digital subsystem supporting vector rates of at least 20 MHz, timing per pin functionality and featuring wide voltage swings in excess of 20 volts per pin. And unlike the legacy systems, today’s digital test systems offer both high performance and wide voltage programming ranges, eliminating the need for multiple test system configurations with different pin or channel board configurations.
  • An integrated analog switching system supporting a hybrid pin architecture allowing multiple analog resources to be routed to any of the tester’s interface pins, providing an “any resource to any test pin” capability and one which provides compatibility with the legacy system’s switching architecture
  • Optional pin multiplexing capability, allowing the test system to support high I/O count boards or multiple ITA configurations as well as maintaining functional compatibility with the legacy test system
  • An integrated software development / run time environment that includes a full-featured test executive, comprehensive system / test program simulation, test program migration tools, and high level signal routing software tools

In addition, adoption of a modular, open architecture as the core platform, allows the system to be expanded or reconfigured based on evolving or changing test requirements – a significant benefit when compared to the legacy ATE systems which were based on a closed and inflexible architecture. Today’s functional test platforms are largely based on the card modular architectures with PXI being the dominant modular standard. With 1500+ products, its compact footprint and high functional density, the PXI platform is ideally suited as the core platform for replacing legacy test systems. 

Integrated PXI System and Subsystem Solutions 

PXI instrumentation and systems have made great advancements since the release of the PXI standard in 1998. With the increasing availability of high performance / high density FPGAs and highly integrated analog electronics, high performance digital functional test subsystems are now a reality. Additionally, the flexibility of the PXI standard has provided vendors the opportunity to design integrated switching subsystems for various functional test applications. By leveraging these technologies and capabilities, PXI-based subsystems and systems are now available which provide the core architecture for replacing a legacy test system. Key features associated with the digital and switching subsystems are detailed below. 

PXI Digital Subsystem

  • 50 MHz vector rate with timing per pin, multiple time sets and a flexible sequencer
  • Compact footprint, offering 32 channels per module and supporting up to 528 channels within a single digital chassis
  • A wide programmable drive / sense voltage range with per pin programmability – providing the flexibility to support a wide range of applications and legacy test system configurations
  • Independent, per pin resource allocation – slew rate, termination, etc. are programmable on a pin basis, maximising flexibility for test program migration
  • Advanced power management capability, resulting in significant reductions in power dissipation and consumption compared to other digital subsystem architectures
PXI Switching Subsystem

  • Modular and expandable analog matrix supporting an internal 16 wire bus for routing analog instrumentation and triggers from an instrument source to the receiver interface
  • Overall signal bandwidth of > 20 MHz with dedicated switching cards offering a bandwidth of over 500 MHz
  • Multiplexed pin configuration that can support over 2200 I/O signals
  • An innovative analog / digital hybrid pin switching architecture, offering a high bandwidth digital signal path and providing “any resource to any pin” functionality
  • Integration of a mass termination interface, providing a cableless receiver interface and resulting in the elimination of thousands of wires
  • A comprehensive software environment for managing overall signal routing 
Both the digital and switching subsystems are incorporated into a compact, 20-slot, 6U PXI chassis (see figure below) which can provide the core subsystem for replacing a legacy test system. This subsystem can provide the basis for a complete, fully integrated functional test system. The core system features:

  • 19 6U PXI peripheral slots supporting either 3U or 6U modules
  • Support for up (9) switching modules, offering over 2200 multiplexed, hybrid test connections
  • Support for up to (8) high performance, high voltage digital modules, supporting up to 256 digital channels which can be routed via the switch modules, providing hybrid capability. Note that the platform also supplies supplementary high voltage power for each digital module, eliminating the need for external power supplies.
  • Integrated SCOUT mass termination receiver providing a reliable, cableless interface to the UUT
  • Integrated high-level switching software, providing end to end signal routing
The PXI chassis only requires a single slot for the controller, maximising the number of peripheral slots. Additionally, any of the peripheral slots can accept 3U or 6U PXI modules, providing further flexibility when configuring the overall system.

The core digital / switching platform can be configured with different switch modules, providing analog / digital switching capability for both baseband and RF applications. These modules provide a combination of matrix and multiplexer capability, offering the flexibility to route signals to / from the backplane, UUT interface, and other external resources. And to efficiently control and manage the switching system, a robust signal routing software environment is provided, offering end to end signal routing which can be incorporated with a variety of Windows-based test executives and APIs.


The open, modular architecture of PXI offers a range of options and capabilities for replacing legacy test systems. And with the availability of performance digital subsystems and innovative switching subsystems, test engineers have the ability to develop and procure replacement systems that offer equivalent functionality to the legacy test systems, as well as offering the flexibility to address future test needs.

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