Instrumentation and Test Expert
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Switching Architectures for Automated Test Equipment (page 1)

One of the most common architectural decisions facing the designer of Automated Test Equipment (ATE) is the switching, or multiplexing, of limited ATE stimulus and measurement resources between multiple test points at the Unit Under Test (UUT). In the abstract these switches and the associated cabling, interface chassis, etc. form a mapping layer between the tester resources and the UUT test points. When deciding on a switching architecture the ATE designer must consider multiple performance criteria including: cost, size, signal quality, reliability and serviceability. This paper looks at the various switching architecture options available to the ATE designer and provides guidance for choosing the best architecture for the application.

I. INTRODUCTION
All Automated Test Equipment (ATE) includes a mapping layer between tester resources and the Unit Under Test (UUT) measurement and stimulation points. The tester resources may include: Digital Multi-Meters (DMM), Source Measurement Units (SMU), Oscilloscopes, LRC meters, digitizers, counter/timers, component analyzers, power supplies and the like. The mapping layer defines the connectivity between the tester resources and the UUT measurement and stimulation points.

Cables provide the most elementary example of a mapping layer. The wires in the cable connect the tester resources to the UUT measurement and stimulation points. Different cable sets can be used to extend the versatility of the tester, but a cable-only mapping solution is only feasible for a very small set of ATE applications.

In most automatic test equipment designs the mapping layer includes switching and multiplexing functionality as shown in Figure 3. This functionality allows a single tester resource, such as a DMM, to be connected to multiple measurement and stimulation points at the UUT. When choosing the switching architecture, the ATE designer is presented two fundamental options: a centralized architecture and a distributed architecture. The centralized architecture typically includes PXI and VXI mainframes that hold relay, matrix and multiplex modules. The mass interconnect is often found in conjunction with a centralized switching architecture. The distributed architecture typically utilizes dedicated switching chassis, such as LXI, physically located in the tester console near where the switching is required. At the limit the distributed architecture locates the switching within custom interface chassis.


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