Traditional electronic test methodologies often have combined different items of discrete test equipment to verify product functionality at the design stage with expensive ATE used to support volume production. Many times, there is little or no correlation in results or even methodologies between the two environments. As a result, the cost and time required to move new products into production have been high.
It has made sense for different stand-alone instruments such as oscilloscopes, arbitrary waveform generators, and logic analyzers to be used at the design and device characterization stage because many times there are specific circuits that must be tested to prove the functionality of the design. On the other hand, integrated ATE has been the solution of choice in volume production because automated test systems have been designed to streamline the fixturing process to increase throughput while verifying part functionality in the typical operating modes. Either way, fixturing the DUT reliably always is a challenge in both the design and the production phases.
Gaps in test coverage can occur in both design verification and production tests because they may be developed by different engineers or with different skill levels or different goals in mind. These gaps can come back to bite companies when products fail. Failure to achieve a smooth transition between the lab and production floor can delay market introduction of a new product, especially in the case of mixed-signal device testing.
Linking Design and Production Test
A better approach uses a test technology that has been built specifically to bridge the product life cycle from design through to production. The physical limitations and risk of problems with reliability and repeatability of test results caused by using instruments such as scopes, signal generators, and logic analyzers can be avoided by selecting a modular instrument platform that provides for robust connections between the instruments and supports a user interface that simplifies the development and application of repeatable test protocols.
In the lab, a modular mixed-signal test system would verify that the output of a DAC is synchronized with what is happening elsewhere in the component—correlating the digital and analog activity. The system would observe a digital pattern on the output or present a digital pattern to the input, looking for linearity in the analog waveform to verify that the converters are producing consistent, continuous results across a full range of analog values.
While an oscilloscope may be used to prove that signal processing is occurring, a more capable mixed-signal test system would be needed to prove out the linearity of the conversions. Large ATE systems can do this, but they’re expensive, and they don’t fit well in the office of a component design engineer. Mixed-signal measuring equipment is an expensive add-on to an ATE system, but if the lab system can be repurposed to the production floor, this added cost can be avoided.
For programming and data logging, a modular test system might interface to a PC in the design lab, connecting via USB or Ethernet. On the production floor, the modular mixed-signal test system would be externally fixtured, connecting directly to a load board where the DUT is mounted while interfacing to a master ATE controller via USB, GPIB, or other industry-standard interface to download test-sequencing commands and upload test results. Whereas a basic functionality test may be sufficient as a production test, the production test needs to produce exactly the same results as the design validation to the extent that the functionality is tested.
Figure 1. ATX7006 Modular Test Instrument
An example of a modular test platform is the ATX7006 manufactured by Applicos BV (Figure 1). The platform supports a combination of instruments including voltage references. The ATX7006 uses a new-generation ATX backplane that’s quieter than typical PXI backplanes, with improved clock signals that are electrically terminated for higher performance with lower noise. The backplane distributes its clock signals as PECL differential pairs. Applicos also offers an ATX-Hybrid version that provides expandability via PXI in addition to ATX, allowing for the addition of PXI instruments when needed.
Additional noise-reducing features include the use of linear power supplies for the analog section and thorough shielding and grounding to maintain analog signal integrity even in a harsh production environment. The digital I/O module provides a low jitter sample clock that is distributed to all the other modules and the DUT. Figure 2 shows a block diagram of the ATX7006.
Figure 2. Block Diagram of the ATX7006
The available generator and digitizer modules cover the range from low-speed high-accuracy testing to high-speed medium-accuracy testing. Auxiliary modules provide all other signals such as reference voltages, supply voltages, clocks, and digital I/O. The ATX7006 measures linearity parameters as well as dynamic parameters, all within the same test setup.
The system controller embedded on a PC-compatible processor within the unit runs the Windows XP-embedded operating system and gives the user full access to the unit’s test features in addition to supporting auto calibration and power-on self-test.
In the lab, the ATX7006 connects to a Windows-based PC; in a production environment, the ATX7006 becomes a slave to the ATE system. In either environment, the system may be accessed via Ethernet, GPIB, or USB. Devices from 4 bits to 24 bits can be tested with a full range of linearity and dynamic choices available. Because the system can be deployed in both design and production environments, it’s a simple matter to correlate results from both.
The ATX7006 can be programmed via commands issued by the attached PC or ATE system or graphically programmed using Applicos’ ATView software (Figure 3). With ATView, setting up a test is as easy as filling in the fields of instrument panels, programming a digital pattern if applicable, and pressing a start button. After the test is complete, the results can be viewed graphically using Applicos’ WaveAnalyzer software, which can show the results of time-domain, frequency-domain, and histogram tests.
Figure 3. Applicos ATView Software Graphical Interface
That leaves the remaining challenge of actually getting signals into and out of the DUT. While this traditionally has been handled by pogo-pin interfaces on the ATE, testing of RF and analog circuitry has posed reliability and repeatability issues when traditional fixturing has been applied.
To address these issues, a transitional fixture, such as one that can test devices in both the lab and the production environment, must be designed with consideration given to the product’s complete road map and the test scenarios that it is likely to require along the way. After identifying the electrical and mechanical demands of the part under the various test conditions, a modular test fixture would be developed.
One leading test-solution provider, Robson Technologies, develops test sockets that consist of two components: the socket body that retains the part and a variety of exchangeable lids designed for use in various test environments. The same test socket can be shared for anything from prototyping to production, from burn-in to failure analysis, and more by switching out the lid. DUT board designs also can account for multi-application use by using a motherboard-to-daughter card interface or offering multiple connector types to directly and indirectly mate with the test system. These techniques allow the modular test fixture and the integrated mixed-signal tester to support a particular product through its full life cycle.
Figure 4 shows such a fixture. Different connector types and components can be added to this simple break-out board, making it an evaluation board for the design lab or a programming board for use with an ATE system. For maximum flexibility, both the top side and back side of the package are accessible without disrupting cable clearances.
Figure 4. Robson Technologies Modular Test Fixture
A purpose-built modular approach to mixed-signal testing can produce consistency of results with the signal coherency required by final production and significant cost savings throughout the design/production cycle.
About the Author
Skip Davis is general manager of Applicos, North America, a subsidiary of Applicos BV of the Netherlands. He is an electronics test and ATE industry veteran with 20 years experience in sales, marketing, and management.