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Serial-data-analyzer family adds enhancements, 11-GHz-bandwidth model
By Dan Strassberg -- EDN, 5/12/2005
LeCroy is the last of the three major high-performance-digital-scope manufacturers to introduce a real-time-sampling scope with a bandwidth greater than 10 GHz. However, LeCroy’s announced bandwidth is somewhat less than the values its competitors Agilent (www.agilent.com) and Tektronix (www.tektronix.com) have been trumpeting: 13 and 15 GHz, respectively. Nevertheless, LeCroy’s director of product management, Mike Lauterbach, PhD, offers a persuasive story about why LeCroy’s target audience—in this case, engineers working with high-bit-rate data streams—should look into his company’s new products and why a bandwidth of 11 GHz can often be more useful than a bandwidth more than one-third greater.
According to Lauterbach, bandwidth isn’t the only important specification in correctly reproducing high-frequency waveforms. As Lauterbach demonstrates, matters of at least equal importance are the linearity of the scope’s phase response versus frequency and the flatness of the amplitude response at frequencies below the –3-dB point. Linear phase versus frequency, also called constant group delay, indicates that an equal amount of time delays all frequency components. When the time delay depends on frequency, the results can be both ugly and misleading. For example, preshoot can appear ahead of voltage steps in waveforms that really exhibit no such anomaly. In some cases, the effect on eye diagrams can be devastating.
The 11-GHz, four-channel SDA 11000, with prices that begin at $105,000, becomes the flagship of the SDA (serial-data-analyzer) series. Like the competing scopes, this instrument operates at full bandwidth when sampling one or two channels in real time and at 6-GHz bandwidth when sampling three or four channels in real time. The maximum sampling rate when all channels are active is 20G samples/sec on each channel. With two channels active, the sampling rate doubles to 40G samples/sec on each active channel. Unlike the competitive instruments, however, the LeCroy units can accommodate memories as deep as 50 million/samples/channel (100 million samples/channel with one or two channels active). Thus, the SDA 11000 can capture records as long as 2.4 msec at the highest sampling rate—50 times the record length of one competitive scope under the same conditions (Picture).
The ASDA-J (advanced serial-data-analysis and -jitter) software package, which is standard in all SDA-series instruments, sports a host of new features, all of which are also available for downloading at no charge to owners of earlier SDA-series units. Features include the Jitter Wizard, jitter filtering, multiple methodologies for total jitter measurement, ISI (intersymbol-interference) plots that permit measurement of data-dependent jitter without a repeating bit pattern, and mask-error-violation locator. This summer, LeCroy expects to announce an active differential probe whose bandwidth is appropriate for the 11-GHz scope.
LeCroy Corp, 1-800-453-2769, www.lecroy.com.
