Evaluation Engineering - 22

AUTOMATED TEST

Editor's note: Evaluation
Engineering's April print issue
features a special report on the
trends, challenges, and new
products available in the high-end
oscilloscopes market. That report
includes commentary from Mike
Martin, senior marketing product
manager at Tektronix. The report
actually included only a very small
portion of Martin's commentary,
which was so in-depth that it
deserved its own article. So, that's
what we've done here, turning
Martin's additional insights into
an article covering the history of
modern high-end oscilloscope
technology and where it's headed.
The Tektronix DPO 73304DX Digital Phosphor Oscilloscope

THE RECENT HISTORY
OF TODAY'S HIGH-END
OSCILLOSCOPE TECHNOLOGY
by Mike Martin
First, let's define a "high-end oscilloscope." There really is no official
definition. Scope vendors arbitrarily draw
a line that allows them to focus on the
applications requiring the highest bandwidth acquisition. The line has moved
considerably over the past decade. Ten
years ago, we used a definition of "highend oscilloscope" that covered a range of
4 GHz to 20 GHz bandwidth. Today, that
definition has changed to a range of
23 GHz to 70 GHz.
When it comes to talking about the biggest trends in high-end oscilloscopes, a
good starting point is to look at the biggest trends in new technology, products,
or system development. For many years,
data communication has driven demand
for high bandwidth acquisition and analysis. This continues to be the case today,
but the increase in performance is stunning. Ten years ago, we were working on
Gen1 and Gen2 standards such as PCIe
and SATA. Data rates were at or below

22

EVALUATION ENGINEERING JUNE 2019

5 Gbps and it was largely held that scope
bandwidth needed to provide coverage
through the 5th harmonic of the fundamental of the signal being tested. A 12.5
GHz scope bandwidth could provide a
good quality acquisition and representation of a 5 Gbps (2.5 GHz fundamental
frequency) NRZ signal.
Since then, data rates have continued
to climb, along with the need for more
bandwidth. As we moved into Gen3 and
Gen4 standards, data rates went up into
the 8 to 16 Gbps range. This drove scope
bandwidth requirements up to 25 GHz
and 33 GHz.
The industry could no longer ignore
external losses caused by cables and fixtures as the margins for passing a test
became tighter. New tools were needed
to de-embed the effects of losses external to the scope, and the scope vendors
responded with features that would allow
the scope to compensate for these effects.
It was also at this point where the old

5th harmonic
goal for scope
bandwidth became
obsolete, as the devices being
tested often did not have the
bandwidth to produce spectral
content at the 5th harmonic.
About the same time, most designers
of high-speed serial links came to depend
on receiver equalization to recover closed
eyes. This resulted in the need to simulate this equalization on the scope, as the
scope acts as a proxy receiver for a lot of
compliance testing for various standards.
Scope vendors have now implemented
robust simulation of receivers, including
flexible Feed Forward Equalization (FFE),
Decision Feedback Equalization (DFE),
and Continuous-Time Linear Equalizer
(CTLE) models.
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