Tuesday, 6 March 2012

 When it comes to the Product of the Year Awards, it’s rare when a company wins the award for the same kind of product two years in a row. Yet this year LeCroy has once again won an award for an oscilloscope, the 45-GHz LabMaster 9 Zi-A, after having won last year for the 30-GHz WaveMaster 830 Zi digital oscilloscope. The reason for this recognition is that, in both years, the company’s products have provided designers with the highest real-time bandwidth, and in the course of a year, LeCroy increased bandwidth by 50%, which happens to also be about 50% greater than what any other real-time scope (RTS) can offer.
To be fair, there are other types of scopes, called sampling scopes, that can capture signals with higher bandwidths. As their name implies, these scopes sample an incoming signal repeatedly, beginning each sampling interval at a slight offset from the previous one, and are thus able to stitch together a picture of a repetitive waveform using several cycles of that waveform. While the input, or front-end, of the scope has a broad enough bandwidth to accept the signal, the actual sampling can’t be done fast enough to satisfy the Nyquist criteria by gathering samples at a rate slightly more than twice the incoming waveform’s maximum frequency. But in an RTS, the sampling rate meets the Nyquist criteria, and both the front-end and sampling satisfy the scope’s stated maximum bandwidth.
Why is this difference so significant? Well, if there’s a high-frequency glitch that occurs rarely, at erratic intervals or only when some rare event happens, a sampling scope is likely to miss it while an RTS isn’t.
An RTS can acquire information about the complex behavior of a signal’s long-term characteristics. Thus an RTS allows designers to correctly measure deterministic jitter so its source can be understood, to apply fast Fourier transforms to waveforms, and to determine why an Eye diagram has gone bad things sampling scopes can’t do.
The performance of both the 830 Zi and the 9 Zi-A relies on a patented technique called Digital Bandwidth Interleaving (DBI), which employs RF hardware to down-convert the high-frequency bands of a signal, then passes both the high- and low-frequency components simultaneously through separate front-end amp­lifiers and ADCs. The two components are then re-combined using digital signal processing.
The DBI technique uses SiGe chips designed by LeCroy and manufactured on IBM lines. For the 9 Zi-A, LeCroy’s designers created a second-generation 7HP SiGe chip with improved performance. And for the new scope, they modularized the design so that a single control unit could oversee multiple high-performance channels, thereby significantly reducing the per-channel cost.
The design is so strong that the company continues to evolve it, introducing the 60-GHz 10 Zi (with 8HP ICs) this January. How far LeCroy can ultimately take scope performance has yet to be determined.


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