Applications that benefit from PXI oscilloscopes

Author : Don Schoenecker, Oscilloscope Product Planner for Keysight

03 May 2018

Oscilloscopes offer a variety of features that are optimised for capturing, displaying and analysing signal waveforms, making them the tool of choice for many benchtop test applications. But as this piece explains, thanks to PXI, ATE environments can now benefit from these same features – including large displays, touch operation, waveform zoom and simple controls that enable the acquisition of difficult-to-capture errors and anomalies.

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Oscilloscopes are primarily used for benchtop applications that take advantage of their large fast displays for viewing waveforms. They provide an intuitive user interface with manual front panel controls, so engineers can easily perform interactive waveform acquisitions and measurements. The large displays allow waveform panning and scaling, both during and after acquisition completion, which is very helpful for debugging. The ability to horizontally split the display to show a zoomed portion of the waveform is commonly supported in scopes and helps search for short anomalies within long acquisitions.

It is not as widely known, however, that PXI scopes can also provide these usability features. Scope technology, migrated to a modular PXI form factor, has retained many typical scope features – just packaged in a smaller footprint and utilising the fast PCIe interfaces to maintain a high display refresh rate. PXI oscilloscopes, which are being used more and more frequently in test applications, use full-featured soft front panels (SFP), allowing the same intuitive scope control and waveform visualisation.

PXI scope SFPs are designed with the same focus on operator usability as benchtop scopes, and even include use of LCD touchscreen display controls. For example, when combined with a touchscreen display, the M924xA scope waveforms can be panned and zoomed with simple touch interactions. The M924xA also supports zone touch triggering, which allows easy setup of difficult-to-define trigger events, simply by drawing a box with your finger. Although the M924xA is a PXI scope, the user interface has been optimised for fast refresh rates.

Digitisers have been used in automated test equipment (ATE) systems and high density multi-channel applications – rather than oscilloscopes – for their high resolution and dynamic range.

Digitisers return acquired data to controllers via fast multi-lane PCIe buses for software processing. The data analysis is performed within application software and displayed at the controller, meaning there is no need for an embedded display. However, measurements like waveform averaging and advance waveform triggers are not possible.

PXI oscilloscopes go beyond a digitiser’s capability and provide measurement tools directly in the module. PXI test systems that benefit from an oscilloscope, rather than a digitiser, include applications that require higher bandwidth, up to 1 GHz. Oscilloscopes provide lower resolution and dynamic range (typically 8 bits), compared to digitisers (which offer 12 to 16-bit resolution) – but for many applications, 8 bits is enough resolution.

Oscilloscopes provide fast waveform sinx/x reconstruction, and corrections for phase and magnitude errors using on-board DSP. Scopes offer many choices for trigger qualifiers, and fast measurements are possible using either on-board capabilities or by using the scope’s application-specific software. PXI scopes are able to take advantage of the large portfolio of scope probing solutions, including passive and active probes for both voltage and current, as well as high voltage, differential and even optical versions probes (the same as desktop oscilloscopes).

PXI oscilloscopes are a benefit in many of the same applications as benchtop scopes, including the following:

- Serial protocol debug and conformance testing, where scopes provide built-in serial protocol triggering and decode capability.

- Serial messaging can be verified, and signal timing and level faults are easily observed.

- Serial bus jitter analysis with clock recovery, where scopes with high sample rates and specialised triggering systems provide serial bus eye and jitter analysis. Infinite persistence display modes allow monitoring eye opening over long durations, without consuming significant memory.

Electronic functional test ATE systems, when scope resolution is sufficient and built-in measurements or advanced triggering can be used.

PXI oscilloscopes, much like benchtop scopes, can add functionality for specific measurements or applications through the use of additional software. For example, waveform generation, frequency response analysis, mask limit testing, video/TV, power analysis, serial decode, and automotive serial triggering and analysis are some of the software options available for the PXI M924xA oscilloscope.

Oscilloscopes are essential when installing, calibrating and troubleshooting electronics. Engineers rely on the ability to see and measure signals within their designs. ATE systems are no exception, and they benefit from applying oscilloscope capabilities in a PXI format – particularly for the applications mentioned.

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