leading edge
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.
economical edge --- EE-Logos.org, Harry Winter
50-GHz-Banwith,
sequential-sampling DSOs
At a $40,000 starting price (two Sampling modules),
the above might be the "bleeding edge" instead, but here is a PC-Card
size DSO, with has nearly identical performance and a cost of only $250 in a
6-GHz, and of $400 in a 50 GHz version. This Card-Scope uses
sequential-sampling too, but the new DS2O method
(two-dimensional Sampling) takes a multitude of samples per repetition, making the DS2O a general-purpose scope for all frequency ranges.
LeCroy calls a similar method NRS, “Near Real-time Sampling” and uses it in
their latest line of DSOs. Another advantage of the DS2O method is
that a digitizing resolution of more than 12 bits is obtained directly and not
by averaging many traces, as with conventional scopes. --- The present 6-GHz
design uses only readily available (commodity) ICs, but with the new Indium
Phosphide (InP) chips bandwidth can easily go beyond 50-GHz, while the power
consumption still remains within the constrains of the USB link. The cost of
only one of the Tektronix TDS8000 would buy 100 of the PC-Card+USB DSOs. But,
of course, a standard PC is needed for the display and to perform the many
post-acquisition tasks listed as features for the TDS8000. There is only one
"small" problem; the PC-Card DSO is a “disruptive technology” and no T&M Company will market
it, because it would “cannibalize” their high-end $40,000
scope market. (In other words, the company looses $40,000 every time they sell
a card-scope and this will get the CEO fired in a few weeks.) This Card-scope
is one of the best examples for a “disruptive
technology” which is a
concept discovery of Professor Clayton M. Christensen, The
Innovator's Dilemma; Harvard School of Business.
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