The Source Measurement Unit (SMU) is gaining popularity due to its ability to integrate programmable power supplies, programmable loads, and DMM functions into one instrument. However, most engineers only seem to understand the impact of SMU on its test system performance and throughput. To achieve the ultimate goal of reducing costs and testing time, the following seven tips allow you to analyze and validate your products faster and more economically.
1. Monitor the startup voltage with an oscilloscopeSMUs that start to measure without reaching a steady state can lead to uncertain test results, but waiting too long can waste valuable time. At this point, you can use an oscilloscope or digitizer to detect the SMU's output level while connecting it to the device under test (DUT) to ensure that the SMU is not stable or ready to start measuring for too short or too long.
Figure 1. Using an oscilloscope or digitizer to detect the SMU's voltage output line to optimize measurement quality and time.
In the past, looking at the output of the SMU required an external oscilloscope with voltage and current probes. The PXIe-4139 Precision System SMU integrates a 1.8 MS/s digitizer, eliminating the need for an external oscilloscope and an external cable - input power can be detected directly through the internal channel. In addition, if any noisy power rails are found during the test, the digitizer can be used for troubleshooting.
Figure 2. The PXIe-4139 Precision System SMU features an integrated digitizer that simplifies the monitoring of output power levels during characterization and verification.
2. Evaluate unit channel price and measurement timeA common way to address the high channel count test requirements is to add a switch or multiplexer between the SMU and the device under test. Although this method is economical, it will serialize the measurement and greatly reduce the work efficiency, because we have to wait for the switch to stabilize before we can start measuring.
Figure 3. Adding SMU channels for high channel count applications increases productivity and greatly reduces measurement time.
The latest improvements in modular SMU channel density have greatly reduced the unit channel price of SMU systems. The 18-slot PXI chassis, such as the PXIe-1085 24 GB/s chassis, can accommodate multiple 4-channel SMUs, such as the PXIe-4141 precision SMU, which forms a 68-channel system in a 19-inch test instrument rack. Thanks to the PXI architecture, all SMUs share the same CPU, trigger line and power supply, which not only helps reduce capital costs, but also reduces floor space costs on the production floor.
Figure 4. High-density PXI SMUs can form up to 68 SMU channels in a single 4U rack.
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