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| Test and Measurement |
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Real-Time Analyzers Peer Into High-Speed Serial Data Streams
| The manufacturer says . . . | ChipCenter's Alex Mendelsohn says . . . | ||||||||||||
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LeCroy Introduces Serial Data Analyzers with X-Stream Technology for Real-Time Analysis of High-speed Complex Data Rates Chestnut Ridge, N.Y.--LeCroy Corporation has introduced three versions of a Serial Data Analyzer, Models SDA 6000 (6 GHz signal capture bandwidth with 75 ps typical rise time for data rates up to 3.5 Gbits/s), SDA 5000 (5 GHz signal capture bandwidth with 90 ps typical rise time for data rates up to 2.5 Gbits/s), and SDA 3000 (3 GHz signal capture bandwidth with 150 ps typical rise time for data rates up to 1.25 Gbits/s). These products make it easy to perform measurements accurately and reliably on high-speed serial data streams. A wide range of target applications includes computer (and computer component) design/validation, testing of high-speed differential electrical links, and capture/analysis of optical signals (up to and including OC-48). The SDAs are designed with a unique user interface that makes the measurement process easy and incorporate LeCroy's patent-pending X-Stream technology, allowing engineers to conduct real-time analysis on high-speed, complex data rates at up to 3.5 Gbits/s. The SDA 6000 features a 20 Gsamples/s maximum sampling rate, 6 GHz input bandwidth, extremely low trigger jitter (<2.5 ps), long acquisition memory, and is designed with a number of specialized analysis tools. In addition to locating signal degradation problems, it can also trace the problem back to its origin, allowing for the comprehensive analysis of serial data streams, telecommunications components, transceiver subassemblies, and transmission systems. The SDA 5000 has many of the same features, with 5 GHz bandwidth inputs. Optional accessories include optical-to-electrical converters and reference receivers whose optical bandwidth is above 4 GHz. The SDAs' high sampling rate and bandwidth allow the Serial Data Analyzer (SDA) to conduct extremely accurate single-shot measurements, which is increasingly important when analyzing the packetized data found in today's optical and electrical serial data systems. With the SDA, data are measured bit by bit so that even the smallest signal anomalies—even those that are <400 ps—can be discovered. In addition to locating the problem, the SDA features advanced eye-diagram analysis and other troubleshooting tools that allow engineers to find the cause of the anomaly so that it can be corrected quickly and easily. LeCroy has designed the SDA series specifically for analyzing the high data rates found in optical and high-speed electrical serial data systems. It can conduct a number of measurements, including jitter, noise, duty cycle, overshoot, undershoot, extinction ratio, Q-factor, mean optical power, and amplitude. Mask testing of SONET/SDH, gigabit Ethernet, and other standards can also be conducted. Not only can these measurements be made accurately, they can be conducted 10 to 100 times faster than with any other similar type of digitizer-based communications analyzer presently on the market. X-Stream Technology The SDA series can conduct precise and complex measurements quickly because of the incorporation of LeCroy's X-Stream technology, an extremely fast streaming architecture for handling and analyzing data. It enables high data throughput even when performing complex measurements and long data arrays. The front end of the X-Stream technology starts with silicon germanium (SiGe) amplifiers and A/D converters that track the incoming signal, digitize it at 10 Gsamples/s on each of four input channels, and stream data to "super fast" CMOS memory chips that can accept the 10 Gbytes/s data rate for up to 48 million points of acquisition. This acquisition memory is a proprietary LeCroy design that performs a variety of operations. It packetizes the data from the A/D converter and transfers the packets in a real-time streaming mode via dual high-speed data buses to the CPU board. At that point, the operating system optimizes the possibility that the analysis algorithms and data packets are resident simultaneously in cache so that calculations can be performed extremely fast. Once the first batch of data arrives at the CPU, a host of display, measurement, and analysis routines can be invoked. Using X-Stream, a long complex waveform can be under analysis by the CPU while the next signal is flowing through the front end of the streaming architecture. The X-Stream technology software algorithms enable data packets and the analysis routines for performing measurements on those packets to be resident simultaneously in the microprocessor cache. This allows complex signal analysis to be conducted on packet data 10 to 100 times faster than older technologies that rely on moving data to the microprocessor from RAM. O/E Converters LeCroy has also designed a series of O/E converters with advanced semiconductor technology. These O/E converters have responsiveness in excess of 1 V/mW covering a wavelength range of 950 nm to 1630 nm, and have optical bandwidths in excess of 4 GHz. They can be used in conjunction with the SDA to test optical communications signals at data rates of 2.5 Gbits/s. Complementing these O/E converters are reference receivers, which use DSP to implement the reference receiver filter. The filter coefficients are computed using the known response of the O/E converter. The O/E response characteristics are stored in a memory chip within the O/E housing. An SDA can dynamically match the response characteristics of the O/E with those of any input channel, allowing the O/E to be moved to any channel on the SDA, moved to another SDA, or have two simultaneous reference receivers on an SDA. None of these capabilities has been previously possible with any test instrument. This offers a tremendous advantage for manufacturing up time since repairs and calibrations can be performed separately on individual components and throughput can be increased by an additional factor of four (by using four reference receivers) in addition to the throughput gains from X-Stream. An added advantage to the digital reference receivers is their ability to support an arbitrary data rate. Jitter Analysis Package One of the most common needs of design/test engineers who work with high-speed circuits is the requirement to quantify the amount of timing jitter in a circuit and to identify/troubleshoot jitter sources. LeCroy is now offering a next-generation timing and jitter analysis package for the WaveMaster series. The SDA comes standard with this jitter package, which allows the user to measure and view jitter in the time, statistical, and frequency domains. It quantifies random vs. deterministic jitter, offers a breakdown of deterministic jitter sources, and estimates the bit error rate. A "golden PLL" is implemented in software to create a local timing reference that is superior to the hardware clock-recovery circuits used in other serial data analyzers. In addition to offering more jitter analysis tools than any other oscilloscope, the WaveMaster also enables the most accurate jitter measurements. This is due to its world-leading 1 ps jitter noise floor, which preserves signal integrity when making jitter measurements better than any other instrument. Unique and Powerful User Interface The powerful user interface in the SDA presents the user with a comprehensive display of the key measurements required by all optical and electrical serial data signals. Eye pattern, jitter, bit error rate, and waveform parameters are displayed in one easy-to-read display. By displaying these key measurements together, the user can quickly determine compliance with standards as well as locate the sources of errors. Design debugging throughput is enhanced by the integrated measurement capability of the SDA since it is not necessary to measure eye pattern, jitter, and bit error rate on separate instruments. The deep memory and fast sampling rate of this instrument allow the capture and display of data sequences as large as 2–23 bits, which enables users to evaluate pattern-dependent problems without the need for special triggers or signal sources. Pricing and Availability
Standard equipment Includes:
O/E Converters
Delivery is 8 weeks ARO. Engineers who would like more information can call 800-4LECROY (800-453-2769) or visit www.lecroy.com. |
Packing fast silicon-germanium (SiGe) front ends, LeCroy's new Serial Data Analyzers (SDAs) provide detailed SVGA-quality application-specific displays of details in fast serial data streams. Bolstered by Windows 2000-based analysis that encompasses a raft of chip-to-chip and board-to-board serial standards (plus custom protocols, too), LeCroy's SDAs should find a home both in the lab and in the field. They'll let you make eye-mask and jitter tests, or parametric tests, or bit-error-rate (BER) measurements for today's serial protocols, both defined and emerging. These include the likes of RapidIO, Fibre Channel, Serial ATA, XAUI, USB 2.0, and PCI-X, to name a few. Although debuting about a year after Tektronix's rollout of the Tek CSA7404, and on the heels of Agilent's 86130A analyzer, LeCroy's LCD-equipped Model SDA 6000 ups the ante with its 6 GHz signal-capture bandwidth and 75 ps rise-time capability. Those specs ensure real-time analysis of data streams at rates up to 3.5 Gbits/s. For validation testing, where bandwidth may not be as important as it is in the lab, integrating LeCroy SDA Family units into functional test suites should be relatively easy, too. To ease the task, LeCroy offers USB (Universal Serial Bus) connectivity, dual Gbit Ethernet links, and IEEE-488 hooks in these analyzers. A Unified Display Significantly, SDA boxes present their measurements in a single display format that conveys just about everything you could wish for in validation and analysis. The instruments also promise single-button data analysis. If you're conversant with Windows, you can drive an SDA using either its built-in SVGA touchscreen or an outboard mouse, all in the familiar Windows environment. That's complemented by a clean front-panel layout that uses illuminated pushbuttons and lighted status indicators. As the press statement indicates, for eye-pattern analysis, SDA analyzers perform a single long acquisition. The generated eye patterns are derived from as many as 8 million consecutive bits. As LeCroy product manager Michael Schnecker notes, to capture 8 million bits you really need more than four samples/bit, and SDAs provide eight. For 8 million bits, that comes to a whopping 64 million samples (or 96 points differentially on two channels). The Golden PLL The SDA measures eye patterns of this continuous acquisition using a software-based so-called golden PLL. In some competing instruments, eye patterns are typically measured using an external data clock, or these systems use clock-recovery circuits to trigger what's essentially a long-persistence oscilloscope. But going this route means that observed jitter at zero crossings can be affected by any trigger jitter itself. Also, since data are collected randomly over many bits, you can have an unfavorable situation that limits the ability to identify pattern-dependent faults. In contrast, the golden PLL essentially eliminates trigger jitter as an error source. Schnecker provides a comparison of eye patterns gleaned from an SDA and a digital storage oscilloscope (DSO). The diagram showing a 1 Gbits/s Fibre Channel signal reveals the additional jitter added to the eye pattern measurement by the cumulative affect of trigger jitter when using a DSO (lower image).
"Since the pattern is the accumulation of many acquisitions over many triggers," points out Schnecker, "the overall contribution is on the order of six times the specified RMS trigger jitter of the DSO or, in this example, about 42 ps. This amount of jitter smears the detail of the actual jitter coming from the source under test." In contrast, an SDA generates only 6 ps of peak-to-peak jitter. Schnecker points out that this is seven times better than using clock recovery. "You really see what transitions look like," he says. Time-interval-error (TIE) measurements using the golden PLL also use the entire data record to generate the reference clock so that you can measure the deviation of the data bits from their ideal locations in time. Also, many published serial standards demand that jitter be measured over certain frequency ranges. The SDA supports these requirements by providing adjustable band-pass filters. The band-pass filters have selectable upper and lower cut-off frequencies. You can apply these to jitter data to yield a filtered total jitter value. Zeroing In For BER analysis, the SDA uses software error detection, where the system's extremely long memory permits the capture of a 223 - 1 bit sequence with up to 12 samples/bit. This type of capability ensures that pattern-dependent errors can be captured. In use, measured bit errors are arranged in a three-dimensional map that shows the bit-error locations as a function of user-defined frames and bits within a frame.
Acquired mask violations can also be directly correlated to an exact bit or bits. You do this by mouse-clicking on a bit location of interest in the displayed eye pattern; the SDA also maintains a table of mask bits, numerically indicating an offending bit's number. Firmware then lets you look at bits both ahead of and after the offending bit. Schnecker says LeCroy will soon offer software that will permit you to scroll forward and back around the offending bit, too.
The SDA's lengthy acquisition record also serves as the input for the measurement of total jitter, as well as random and deterministic jitter. The latter is gleaned from duty-cycle distortion, inter-symbol interference, and periodic jitter. Jitter is also measured in terms of its frequency components; filtering of the jitter spectrum is used to measure the contributions from specific sources. Clock and timing measurements include period and half-period jitter, too.
For waveshape analysis, the SDA's fast front end reveals rise and fall times, and lets you see attributes such as overshoot. For optical signals, you can see the extinction ratio and the Q factor.
O/E Modules Coming Soon
Speaking of optical measurement, LeCroy is offering an optical reference receiver, and is about to offer two optical-to-electrical converter (O/Es) modules. Although the press statement indicates that the Model OE425M and OE455M modules are priced and ready to ship, Schnecker says beta testers only will have them by early November. LeCroy isn't taking general orders for these O/Es now, as the company is still temperature-testing and characterizing these options.
When they do debut, they will use DSP-based filtering. This, in combination with stored calibration data in an O/E probe, will generate 4th order Bessel-Thompson low-pass filtering for the probe-scope combination. What's nifty is that calibration will be valid on any channel of the instrument—and stay valid even if a probe is moved to a different SDA or to an o'scope. You'll be able to move these O/E converters from channel to channel, or between instruments without having to recalibrate.
A Cached Architecture
LeCroy's press statement also discusses the company's X-Stream architecture. As you can tell from reading the release, it's a very fast streaming technique that really leverages the SDA's SiGe front-end amplifiers and 20 Gsamples/s A/D converters. The X-Stream's fast sampling works on each of the instruments' four input channels, and SiGe triggering circuits can lock onto signals up to 5 GHz.
In operation, the system's acquisition memory packetizes the data pouring out of the front-end A/D converters, and then streams packets (about 1000 points in size each) to the system's Pentium III microprocessor. Sidestepping the limitations of Windows, LeCroy codesmiths put both the data packets and their associated analysis algorithms into Level 1 cache on the Pentium chip. As such, the calculations are executed from fast on-chip static RAM.
LeCroy claims that X-Stream's simultaneously resident analysis code and data permits data crunching to be conducted ten to 100 times faster than previous techniques that moved captured data from RAM to a microprocessor. In the SDA, there's no fetching of instructions from system RAM, and the Pentium processes the signals while newer signals are flowing through the SDA's front end.
Note that you can readily customize SDA instruments, too, thanks to a COM-based architecture within Windows 2000. The SDA uses more than 400 COM objects, and you can write scripts in whatever programming environment you prefer, including VisualBASIC, MatLab, Mathcad, and Excel.
Once written, scripts can be integrated into the SDA's processing chain without requiring that you run a different program, or set up communications between the SDA and other software. You won't have to create new reference waveforms, or transfer data files.
Lastly, while the top-end SDA6000 model touts a 20 Gsamples/s sampling rate and a 6 GHz input bandwidth, lower bandwidth SDA family members can cost-effectively accommodate less stringent applications, too. LeCroy's press statement refers to the SDA 3000 model, for example (but doesn't mention its $47,990 price). For that you can analyze bit streams as fast as 1.25 Gbits/s.
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