The pace of change in the electronics industry requires that successful companies focus on maximizing the value-added content of their products. It makes no difference if your product is a satellite terminal, a heart pacemaker, or a computer central processing unit—the same principles apply. The price commanded by your product is not determined by the cost to build and test it, but by the value it has to the customer.
Under these constraints, ATE adds to the cost of the product, but does not add value per se. Deleting the ATE function would allow faulty products to reach the end user where they are much more expensive to repair or replace, not to mention the effect it would have on the company’s reputation.
So ATE is a necessity for a high tech company, but it may not represent its core competency. Outsourcing the design and construction of ATE frees up valuable engineering resources that can be applied to product design and enhancement.
Digital Functional Test System
To illustrate the importance of outsourcing, consider the VXI-based system that was designed and built by Racal Instruments and Vektrex Electronic Systems to perform 50 MHz functional board testing. These boards process digital and video signals and are part of an inspection system used in semiconductor fabrication facilities.
Figure 1 is a block diagram of the digital functional test (DFT) system. It consists of:
High-Speed Digital Data Input First-In First-Out (FIFO) Buffers—a series of parallel memory banks that receives, stores, and transmits high-speed digital information for processing by the high-speed processor.
Transceivers—buffers for control, timing, and signal- integrity conditioning.
High-Speed Processor—the controller that manages data manipulation at rates up to the maximum speed of the DFT. The processor:
Receives and stores DFT digital stimulus.
Receives, stores, and executes VMEbus instructions from the DFT.
Receives, stores, and manipulates digital coded signals from the DFT to the analog input circuits.
Executes instructions stored in ROM.
Outputs digital response to the DFT through the high-speed digital data output FIFOs and analog output circuits.
High-Speed Memory and ROM—volatile and non-volatile memory to store digital information required by the processor.
High-Speed Digital Data Output FIFOs—a series of parallel memory banks that receives, stores, and transmits high-speed digital information for processing by analog output circuits after modification by the Lookup Table.
Lookup Table—an operation that modifies the digital output of the high-speed digital data output FIFOs for conversion by the analog output circuits.
VMEbus FIFOs—standard VMEbus interface circuitry for converting DFT-generated VME signals to processor instructions or data for use by the processor.
Control Logic—circuitry that coordinates the sequence of board operation in concert with the processor and facilitates communications of inputs and outputs with the DFT.
State and Error Indicators—status displays that communicate the current state of the board and indicate any errors to the DFT.
The DFT consists of two components. The standard test resource contains the VXI chassis, DC power supplies, power controllers, video generators and video measurement units, and a Pentium-based PC controller (Figure 2).
The second part of the system is the fixture. The fixture interfaces the standard test resource to the UUT. It contains all of the unique electronics and mechanical interfaces that are peculiar to the UUT. The fixture also includes the personality module that identifies the UUT to the controller, which selects the appropriate test program.
Figure 3 is a block diagram of the fixture. The standard test resource can be used for several different UUTs by changing the fixture. This flexibility allows the test capacity to be scaled to production requirements. As production demands increase, the standard test resource could be duplicated, adding additional capacity.
The fixture provides a VME interface to the UUT. VME is the original bus architecture on which VXI is based. VXI was chosen as the foundation for the standard test resource because it supports flexible switching solutions, static and dynamic digital I/O, digital multimeters, and frequency counters.
VXI offers a wide variety of hardware for future expansion. The VXI-to-VME transition is achieved using a National Instruments MXI-to-VME interface routed through a quick-connect TTI-Testron interface. A TTL-to-differential ECL interface also is contained in the fixture.
DC power for the fixture is supplied via power supplies located within the fixture itself. The supplies are remotely controlled via 115 VAC through the TTI-Testron interface. Fans are included to provide cooling to the UUT.
The DFT is controlled by a Pentium Pro™-based PC running on Windows NT 4.0. The controller interfaces with a Racal Instruments 1261B VXI Mainframe via a National Instruments PCI/MXI-II Slot-0 controller. Also included is a GPIB interface, a four-channel RS-232-C serial interface, a Joint Test Action Group (JTAG) interface, and a PCI-based RGB video frame grabber.
The parallel port provides a second JTAG interface, and the serial port supplies RS-232 communications with the fixture. A PCI-based Ethernet port connects the test system to the computer system.
VXI Subsystem
The VXI mainframe supports a Vektrex Programmable Clock Generator and Racal Instruments’ 2251A Frequency Counter, 1260-14C Digital Input/Output Module, and 1260-38 High-Density Multiplexer Module. An Interface Technology SR5000 Digital Test Subsystem and an HP E1412A Digital Multimeter also are provided.
The PC controller interfaces with the VXI mainframe via a National Instruments PCI-to-MXI kit. A National Instruments MXI-to-VME kit provides the VME interface to the UUT. All signals are routed to the fixture via the TTI-Testron interface.
Software Strategy
A mixture of diagnostic testing is performed using the VMEbus and bed-of-nails test-point access. The VMEbus interface provides register access to the UUT. The bed-of-nails interface supplies power and clocks to the UUT, sends and receives video to and from the UUT, and offers functional test patterns to test the digital circuitry that cannot be tested through the VMEbus interface.
When the UUT operates under normal circumstances, it is controlled via the VMEbus. The tester control is centered on a rack-mounted PC, so a PCI-MXI and a MXI-VME translator are used to allow the PC to access registers on the UUT’s VME interface. This interface stimulates many digital portions on the UUT, such as FIFOs, registers, digital comparators, and memory for basic diagnostic testing.
Diagnostic tests also are run via the bed-of-nails interface. The Interface Technology SR5000 Pattern Generators interface to digital test nodes via transparent data latches and TTL-to-ECL translators, where necessary.
The UUT’s 24-bit digital comparator is tested using the VMEbus to write to the comparator and the SR5000 to measure the output via the bed-of-nails interface. ICs with JTAG boundary scan support can be tested via the bed-of-nails interface by the JTAG card in the PC.
Analog circuitry also is tested for functionality via the bed-of-nails interface. Video signals are routed into and out of the UUT through this interface. The video output, after it is processed by the UUT, is converted into an RGB signal that can be digitized by the frame grabber for comparison to a standard. UUT voltage-regulator outputs and other analog points are multiplexed into the DMM.
Conclusion
The DFT has helped the customer shorten test-cycle time and improve delivery of its product. With the versatile and cost-effective design of the DFT, the same hardware can test different board designs and other products in the future. This is made possible by the DFT’s hybrid detachable test fixture and application-specific software.
About the Authors
Ted Miller is a consultant specializing in operations and marketing. He earned a B.S. degree in electrical engineering and a master’s degree in business administration from the University of Southern California. Mr. Miller has held positions in marketing and operations at Hewlett-Packard, Racal Instruments, Raytheon, and Toyota Motor Corp. 1350 Dunning Dr., Laguna Beach, CA 92651, (714) 497-2358.
Thomas J. Gallagher is the director of Custom Systems at Vektrex Electronic Systems. He has a bachelor’s degree in electrical engineering from Northeastern University and a master’s degree in computer engineering from Boston University. Vektrex Electronic Systems, 8675 Miralani Dr., San Diego, CA 92126, (619) 578-6787, www.vektrex.com.
Copyright 1998 Nelson Publishing Inc.
July 1998
