When characterizing or testing a design, you may need to use multiple test and measurement devices together for full test coverage. Often this necessity presents challenges. Engineers must overcome system integration issues from impedance mismatches, propagation delays, and noise between measurement devices. This costs valuable time to make test devices work as one system. A common workaround is to add software delays to account for switching times, unknown propagation delays, or other timing uncertainties, thus increasing test times. Because of these challenges, timing and synchronization are often not implemented at the sacrifice of measurement accuracy, development time, and test times. However, off-the-shelf solutions exist.
The PXI hardware platform, for example, is ideal for system use. Timing and synchronization features are built into the platform, with defined software standards and hardware triggers, reference clocks, sample clocks, and events shared along a common backplane. With traditional instrumentation, there's often an option for a higher precision reference clock, but only one instrument benefits from the higher precision. In PXI, you can import a high-precision reference into the chassis, and all the modules in the chassis can benefit from the higher stability. To illustrate the point, when using a PXI arbitrary waveform generator to generate a 10 MHz signal, the error is 0.00046% when using the standard oscillator. If you replace the PXI backplane reference clock with a high-stability reference, such as an oven-controlled crystal oscillator, the error is 0.0000009%—a 500X improvement. Other devices in the system can take advantage of the improved oscillator. In PXI, you upgrade the oscillator once, and all devices in the system benefit.
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The building blocks of timing and synchronization.
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PXI provides other resources for timing and synchronization. When validating an A/D converter, for example, a deterministic time correlation between the stimulus and response is imperative. You could easily synchronize the arbitrary waveform generator to a high-speed digitizer or digital device through a shared trigger and clock with PXI. Likewise, the digitizer could send an event to the arb indicating that it's done with the acquisition. This way you only acquire the data you need when you need it.
Software is another important factor critical to timing and synchronization. A powerful, easy-to-use software, such as National Instruments LabVIEW, is integral to make multiple test devices run as one single system. Software is how you tell your measurement devices what sample clock to use, where to get a trigger, or when to start acquiring data. LabVIEW includes powerful functions for timing and synchronization and combined with PXI, you can reduce test time and system development throughout the design cycle.
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