Sampling-scope bandwidth hits 100 GHz at 10M samples/sec
By Dan Strassberg -- EDN, April 14, 2005
With the introduction of the WaveExpert 9000 and SDA 100G, LeCroy Corp joins Agilent (www.agilent.com) and Tektronix (www.tektronix.com) in offering scopes in a category that used to be called sequential equivalent-time sampling. LeCroy previously has offered only real-time-sampling digital scopes, some of which also incorporate RIS (random-interleaved sampling). With the scopes’ 10M-sample/sec acquisition rate—at least 50 times as fast as that of other sequential-sampling scopes—and the addition of several sampling modes, including RIS, that are new to such scopes, the term “sequential equivalent-time sampling” no longer fits. LeCroy prefers to call the new units simply “sampling scopes,” even though that description can lead to confusion with real-time-sampling scopes.
The new instruments feature optional 100-GHz bandwidth and a patent-applied-for CIS (coherent-interleaved-sampling) mode, which enables capturing and displaying of long serial-data waveforms with no need for an external pattern trigger (Picture). In addition, the scopes can produce TDR (time-domain-reflectometry) pulses that have 20-psec incident rise times, which LeCroy says are 50% faster than those of other instruments.
Unlike traditional samplers, which produce an approximately gaussian sampling aperture, the monolithic sampling head, whose sampling-strobe-generation circuit employs a patented NLTL (nonlinear-transmission line), creates a rectangular aperture, enabling the 100-GHz bandwidth. According to LeCroy Product Manager Mike Schnecker, “Not only does the monolithic construction allow much higher sampling rates than do older discrete designs, but also the rectangular strobe reduces jitter, more accurately controls bandwidth, and provides nearly 100% efficiency.”
The CIS timebase derives the sampling gate by phase-locking to the clock signal, a technique that allows high sampling rates and precise tracking of the signal bit rate. The coherent nature of the sampling gate allows the system to lock to the data pattern simply by knowing its length. The scope can measure and process the resulting waveform in the same way that real-time scopes process traces. The RIS mode, which LeCroy calls a first in this type of instrument, allows the measurement of pulsed signals without the use of an external trigger signal.
LeCroy designed the WaveExpert 9000 and SDA 100G to meet the measurement needs of high-speed designs whose serial-data rates far exceed 3 Gbps and require high-bandwidth instruments that can measure fast-rise-time signals. The new instruments feature real-time waveform displays and a jitter-measurement mode that measures total jitter as well as random and deterministic jitter components. The basic waveform memory in this mode is 4M samples per channel, which enables jitter-component breakdown and equalization on long serial-data patterns. Memory is expandable to 2G samples per channel, enabling the oscilloscopes to capture, display, and measure data patterns that are millions of bits long.
The $21,500 WaveExpert 9000 aims at general-purpose signal-integrity applications, including TDR and eye-pattern analysis. LeCroy also offers a jitter- and eye-measurement package, with which, says Schnecker, the WaveExpert 9000 can analyze jitter in accordance with many standards and can perform eye-pattern analysis faster than any competitive sampling scope. The $41,500 SDA 100G targets serial-data applications and includes the CIS timebase as well as the full jitter-measurement package.
In addition to the two mainframes, LeCroy has announced several plug-in modules for measuring electrical or optical signals. The electrical-input modules, which are priced from $7000 to $50,000, have bandwidths of 20, 30, 50, 70, and 100 GHz, whereas the optical modules, which are priced at $25,000 and $45,000, have bandwidths of 25 and 50 GHz. The $7000, 20-GHz-bandwidth electrical module incorporates the TDR capability. Schnecker predicts that the modular design will let users configure the WaveExpert 9000 and SDA 100G to meet testing needs without sacrificing the flexibility to extend capabilities as analysis requirements expand. For example, the initial electrical modules have single-ended inputs, but LeCroy expects to soon be able to announce differential-input electrical modules.
The instruments include a full set of compliance masks as well as measurements for both RZ (return-to-zero) and NRZ (non-RZ) signaling formats. The CIS timebase enables a rapid mask-testing feature that compares as many as 3M samples/sec with a compliance mask—a 30-times speed improvement over other mask-testing approaches—and provides, says Schnecker, the highest level of confidence in measurement accuracy.
LeCroy Corp, 1-800-453-2769, www.lecroy.com.
