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Figure 6 shows a “Pass Through” configuration. This design takes instruments in the system and connects them to the ITA. To connect the instruments to signal management, they are wired internal to the test fixture. This configuration is the most flexible as you can reconfigure the test system by changing test fixtures. The downside is that wiring lengths are much longer. In addition, each signal goes through the ITA up to three times before being connected to the UUT, inducing losses and affects signal integrity. Figure 7 shows a hard-wired configuration. In this setup, the instruments are wired directly into the signal management system. This design keeps signal lengths manageable and assures the best signal integrity. The downside is that re-configuration requires redesign of the Fig. 4: A switching matrix makes the appropriate connections. test system, limiting the flexibility. Selecting a mass interconnect Speaking of interconnections, if your test system will be testing many different UUTs, consider a Mass Interconnect system, also called ITA (Interface test Adapter). A well designed ITA system will get you consistent results and an easy way to change UUTs. But keep in mind that you have added addi- The PX8000 brings a new dimension to power analysis with the introduction of high-accuracy time-based measurement. Combining Yokogawa’s leadership in power measurement with its proven expertise in oscilloscope design, the PX8000 offers futureproof technology for the next generation of design engineers. See more at: tmi.yokogawa.com/px8000 or contact +31 88 464 1429 signals create unwanted “antennas”, or “Stub Lengths”, that limit the frequency response of the matrix. Another thing to consider when using a matrix is the added cost. The ability to make all possible connections between a UUT and an instrument or series of instruments requires a lot of relays! For example, if you want to connect a four-wire measurement device to 96 possible connections, you’ll need up to1,536 relays! System configuration Now we have a good understanding of the test requirements and the signal switching resources available. Let’s consider how we can implement signal management. If you look at figure 5, you see a typical system block diagram – the PC controller and stimulus and response instrumentation. The signal management subsystem sits in between the ITA (Interface Test Adapter) and the instrumentation. The first issue when you design a test system is how the instrumentation interconnects between the UUT and the Signal Management System. Two different architectures are shown here. Where power meets precision PX8000 Precision Power Scope Precision Making Time-based precision measurement of power inputs Packed with power-specifi c analysis capabilities Manufactured to the highest standards of quality and reliability Highly fl exible confi guration Familiar and user-friendly interface www.electronics-eetimes.com Electronic Engineering Times Europe April 2014 27


EETE APR 2014
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