Using PXI Express to shorten time to market for consumer electronics
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PXI Express delivers higher bandwidth, increasing options for designers to capture and analyze data. In the application of consumer electronics testing, some of the benefits of using PXI Express-based instrumentation to improve testing and shorten development time are explored.
[ad]Every day, breaking technology or a hot new feature is introduced to the consumer electronics market. From TVs to cell phones, DVD players to navigation systems, consumers are constantly demanding more functionality from their electronics. In this environment, device manufacturers must find ways to shorten time to market to stay ahead of the competition. Being first to market with new technology can translate into big payoffs, while delays in product release can mean the difference between success and failure.
With the introduction of PXI Express to the PXI platform, consumer electronics manufacturers can address these challenges by simplifying the design process and reducing product test time. PCI Express technology added great improvements to the industry standard PCI bus. PCI Express maintains software compatibility with PCI, but significantly increases the bandwidth by replacing the 133 MB parallel bus with a 2.5 GB , high-speed serial bus. PCI Express sends data through lanes that offer 250 MB of bandwidth in each direction. Another benefit is that multiple lanes can be grouped together as x1 (by one), x4, x8, and x16 links. The x1 and x4 PCI Express links are most common for instrument-class hardware and provide 250 MB and 1 GB (four lanes at 250 MB ) of dedicated throughput.
Since PXI Express leverages PCI Express technology, an instrument in a PXI Express slot benefits from the dedicated bandwidth to achieve high transfer rates over the bus. Dedicated bandwidth also means that overall system throughput increases as more instruments are added to the chassis.
Replacing simulations with real world signals Designers might ask themselves how a high bandwidth bus actually benefits electronics design testing. One of the biggest benefits of PXI Express is the ability to test devices with real signals instead of simulated waveforms. Consider the case of testing a new wireless design. The traditional approach is to use simulated waveforms covering common test cases ranging from the ideal test signal to a test signal with standard impairments such as fading, echoes, and white Gaussian noise. While this approach is common for testing wireless devices, the test does not accurately cover all the scenarios that occur in the real world to ensure success in the deployed product. The other option would be to create a mobile laboratory with all the necessary instrumentation to drive the wireless device around and analyze the actual response in different environments such as inclement weather or around tall buildings. While the test signals are much more realistic in this case, this approach is not practical because of the high cost and amount of time consumed.
What if there was an easy way to bring the real world to the design lab? With PXI Express, designers can combine the benefits of both previous approaches. Tests can be performed by recording the RF spectrum of interest in all of the use conditions of interest, and then bring those real-world signals back to the lab for more realistic tests. This means signals only need to be acquired once, and then can be used for multiple design iterations of the product, with all of the necessary test equipment in the lab close at hand when needed. Using a high-bandwidth bus such as PCI Express enables the test instruments to stream data to or from the host computer memory or hard disk storage. At data rates in the hundreds of megabytes per second, host computer memory provides data streaming capabilities up to a few seconds, while larger capacity disk drive solutions can extend streaming for several hours. While typical laptop and desktop hard drives can only sustain data rates around 20-30 MB , RAID (Redundant Array of Independent Disks) systems can stream the data across multiple hard drives enabling much higher sustained read and write speeds. For example, National Instruments HDD-8264 external RAID array with twelve 250 MB hard drives (3 terabytes of total storage) can sustain read and write speeds over 600 MB for hours (see Figure 1). Even with costly deep memory options, traditional instrumentation can only sustain the acquisition or generation of signals for several hundred milliseconds. PXI Express modular instrumentation and RAID technology create the ideal solution for a streaming system where the real -world environment is recorded and data used to test a wireless design under real world conditions.
Video testing PXI Express provides benefits for analog and digital video testing as well. For example, a DVD player has a myriad of analog and digital outputs that must be verified before shipping. Because video waveforms can be especially large for even a few frames of test data, engineers are often presented with the same dilemma in the wireless device scenario previously mentioned. Tradeoffs must be considered when creating test systems to validate operation of the DVD player. Some systems run tests with only a few frames of data, while others use just a single frame. These systems can prevent the best product from getting to the customer, since an error in a decompression or decoding algorithm might not manifest itself within seconds or even minutes of a moving test pattern. Another option some manufacturers use is for someone to watch a few seconds of every DVD player output and give each unit a manual pass or fail. Since the test does not use instrument memory to store a pattern, longer outputs can be observed, but this method has the obvious downside of poor efficiency. It also has lower accuracy since the human eye cannot see all the pixel errors that occur on a video display. Again, by using PXI Express instruments and RAID technology, these problems can be avoided with a more efficient and faster test system. For example, with National Instruments PXIe-6537 50 MH z, high speed digital I/O module, all 32 channels can be streamed to or from disk at the full data rate of 200 MB (see Figure 2) . Also, DVI images can be continuously generated or acquired for minutes or even hours to perform accurate digital video pixilation tests.
For analog video, capturing the composite or component video signals can be performed with National Instruments PXIe-5122 14-bit, high-speed digitizer with video triggering (see Figure 3). Running at its maximum sample rate of 100 ms , data from both simultaneously-sampled channels can be acquired continuously at the full data rate of 400 MB , sent across the PXI Express backplane, and transferred to RAID storage.
PXI Express and RAID provide “infinite memory” PXI Express and RAID technology provide benefits to many other areas of consumer electronics testing. The high bandwidth, PXI Express backplane provides a high-speed connection between instruments and storage media such as RAID systems. This results in effectively infinite onboard memory for instruments, since high sample rates can be maintained for minutes or even hours of an acquisition or generation. Recording real-world signals for playback in the lab decreases costs and provides a better-tested product for the consumer. Real world test waveforms reveal potential design flaws that would otherwise go undetected and provide a more accurate measurement of how the final product will perform once it is deployed.
Since PXI Express is an extension of the PXI platform, it still provides benefits that have already improved many consumer electronics test systems, such as:
- capability to upgrade systems to meet new testing needs as technology becomes available
- small footprint
- synchronization between channels of different instruments
- ability to perform custom measurements
By combining new functionality with the newest features, the PXI platform is continuing to enable better and faster consumer electronics tests.
