Digital Scopes Battle Jitter With 100-GHz Bandwidth

These instruments leverage a new sampling mode, a fast acquisition rate, and real-time waveform displays to satisfy the measurement needs of todays high-speed designs.

Serial data rates are continuing to increase, further emphasizing the critical nature of accurate and repeatable jitter measurements. To provide insight into such complex signal-integrity issues, the WaveExpert 9000 from LeCroy (Chestnut Ridge, NY) offers a fast sampling rate and interleaved sampling time base. With these features, a complete signal waveform can be displayed and measured

without a separate pattern trigger. A second oscilloscope from the company, the SDA 100G, makes serial-data and jitter measurements standard. These measurements promise to deliver comprehensive analysis including total, random, and deterministic jitter as well as the component parts of deterministic jitter.

The two high-performance oscilloscopes flaunt 100 GHz of bandwidth. A new monolithic sampling head design enables this impressive performance. The design uses a nonlinear transmission line (NLTL) in the sampling strobe generating circuit, thereby creating a rectangular sampling pulse instead of the approximate Gaussian apertures of other sampling scopes.

In addition, the oscilloscopes' coherent interleaved sampling mode enables the capture and display of very long serial-data waveforms. The sampling gate allows the system to lock to the data pattern just by knowing its length. The resulting waveform can be measured and processed in the same manner as a real-time oscilloscope trace. Thanks to the coherent-interleaved-sampling mode (CIS), the signals can be measured without an external trigger signal.

The WaveExpert 9000 (see figure) and SDA 100G also boast an acquisition rate of 10 MSamples/s. Their 4-Mpoint waveform memory expands to 512 Mpoints, extending their measurement capability to the longest data patterns. For time-domain-reflectometry (TDR) measurements—a technique for evaluating interconnects and backplanes—the oscilloscopes can output a TDR pulse with a 20-ps incident rise time. The instruments include jitter and eye-pattern measurement software as well as an easy-to-use, real-time oscilloscope interface with a full set of math functions and parameters.

The WaveExpert 9000 targets general-purpose signal-integrity applications. In contrast, the SDA 100G is ideally suited for serial-data applications. It includes the coherent interleaved time base as well as a full jitter application package. Aside from the two mainframes, several plug-in modules are available for measuring electrical or optical signals. The electrical modules have bandwidths of 20, 30, 50, 70, and 100 GHz. The optical modules have bandwidths of 10, 25, and 50 GHz. The instruments include a full set of compliance masks along with measurements for RZ and NRZ signaling formats. LeCroy Corp., 700 Chestnut Ridge Rd., Chestnut Ridge, NY 10977-6499; (914) 425-2000, Internet:

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