leading edge January 20, 2000 EDN, Dan Strassberg [excerpts only]

50-GHz-bandwidth, sequential-sampling

DSOs test 10-Gbps network components

Of ALL DIGITAL SCOPES, only sequential equivalent-time-sampling instruments offer bandwidths as high as 50 GHz. This capability makes such scopes the instruments of choice in applications of rapidly growing importance---electro-optics, for example.

Yet, because these scopes work only with repetitive waveforms and take just one sample during each input-signal iteration, they lack the quick response of lower bandwidth, real-time -and random-sampling instruments. This characteristic limits Sequential-sampling scopes largely to applications that need extraordinary bandwidth. -------- To address the requirements of engineers, who develop components for networks that transmit data at speeds as high as10Gbps, Tektronix has introduced a family of sequential-sampling scopes. ...(TDS8000 and CDS8000) ------- Each scope accommodates four sampling modules. Five modules provide a variety of electrical interfaces. Three more optical-sampling modules support the OC-12/STM4, OC-48/STM16, OC-192/STM64, Gigabit Ethernet, and Fibre Channel standards. ... The TDS-8000 cost $19,000. Prices for electrical-sampling modules (15GHz) begin at $10,500 each; prices for optical-sampling modules begin at $17,000 each.

Tektronix Inc, 1-800-426-2200, www.tektronix.com.

  A NEW T&M FLAGSHIP PERSONAL INSTRUMENTS, Harry Winter

At a $30,000 starting price, the above might be the "bleeding edge" instead. But here is a PC-Card DSO, which has very similar performance and can be marketed for $400 in a 6-GHz, and for less than $800 in a 50 GHz version. And while this Card-Scope uses the same sequential-sampling concept, a new DIS method (Dual Incremental Sampling) takes many samples per repetition just as random-sampling does, but it is even faster responding. This characteristic makes this Card DSO a general-purpose scope for all frequency ranges. Another advantage of the DIS method is that a digitizing resolution of up to 12 bits is obtained directly, not by averaging many traces, as it is done with conventional scopes. (For Specification go -> Tricorder2G )

The present 6-GHz design uses only readily available (commodity) ICs, but with the new IndiumPhosphide (InP) chips bandwidth can go beyond 50-GHz, while the power consumption still remains within the constrains of the PCMCIA format. The cost of only one of the Tektronix TDS8000 would buy 30 of the PC-Card DSOs. But of course, there needs to be a standard PC, which will also perform the many post-acquisition task listed as features for the TDS8000. - There is only one "small" problem, no T&M company will market it!

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