Evaluation Engineering - 13

Low/mid-density tradeoffs
Tradeoffs exist between low/mid-density
switches and high-density. What are the
key advantages/tradeoffs between low/
mid-density and high-density switching
systems?
Stasonis, Pickering Interfaces: As referenced above, it is a tradeoff of specification versus density. Of course, as stated,
much of this is applications-driven. And
in a modular platform like PXI, the limited slot space in a chassis means that
test-system designers are looking at the
densest switching system that meets
their requirements. Too many slots
used for switching may mean that the
test engineer must specify an additional
PXI chassis, which adds costs and takes
up rack space. This is one of the reasons
Pickering designed a series of low-cost 2-,
4-, and 6-slot LXI/USB chassis to accommodate additional switching slots when
there is no space to supply the switching
necessary in a single PXI chassis.
Semancik, Marvin Test Solutions:
Without having the formfactor or definition of low/medium/high-density stated,
this basically comes down to a
physics and electrical engineering question.

Lower density switching typically means
fewer relays for a specific board formfactor. This means the design has more layout
space for traces and shielding, which can
improve bandwidth, noise, and cross-talk
specifications. Current-carrying performance can also be increased with larger
footprint/higher current relays, but again,
density will be compromised.
Higher density switching obviously
increases the overall channel count, but
it will impact the rated bandwidth, noise
specifications, and the impact from unterminated stubs, as trace placement and
spacing becomes more critical. There are
definite advantages with high-density
switching, such as being able to switch
any resource to any pin and having
the ability to extend this capability to
thousands of channels for demanding
applications."

Stasonis, Pickering Interfaces: In modular
test, connector technology can be a challenge. For example, PXI's 0.8-in.-wide front
panel limits what kind of connectors can
be used, whether it is high power or high
frequency. The other option is a 2-slot-wide
front panel, which takes up valuable slot
space. Connector designers need to step up
and improve present connector technology
to get smaller while still staying robust.

Alderson, Universal Switching Corp.: The
most common tradeoff between low/midand high-density switching has been
crosstalk isolation, but given that problem, USC has continued to focus our product development in this strategic area.
We have increased grounding, increased
shielding, and utilized EMI gasketing for
a variety of our products with impressive
results. As product frequency capability
increases, good isolation becomes even
more critical.

Brown, Tektronix: Increasing switching
speed helps to reduce overall test time.
One way in which we realize this is by
moving away from traditional electromechanical relay switching to using either
reed or solid-state relays. A user may have
to consider some of the tradeoffs when it
comes to adopting these faster-switching
means, which could include settling for
a lower voltage threshold per channel, a
lower current capacity, or both.
One of the additional hurdles we
continue to address is the ability of
switching systems to work well with
other pieces of test equipment in a rack.
Traditionally there are some external
trigger lines-input and output-that are
used to sequence operations between a
switch and another piece of equipment.
As the demand for shorter test times
increases, we either respond with lower
trigger latencies or find other means to
expedite the instrument interactions.
Most of our newer systems boast < 500ns latency on external input/output
triggering, but we can achieve the same
results with digital I/O and Keithley's
TSP-Link interface.

Josh Brown, Keithley factory applications engineer, Tektronix: A denser system may end up having greater switched
or carry-current restrictions. Along with
many more switching channels, a highdensity system tends to also want to try
to offer a small footprint, allowing a user
to maximize their rack or bench space.
However, there is only so much you can
pack onto a printed-circuit board before
surface area and physics remind you of
your limitations. A lower-density system
might offer higher signal levels; you will
simply have less of them to work with.

Key technologies
Marvin Test Solutions
GX6188 matrix switch card.

What key technology or innovation challenges are manufacturers or marketers
of low/mid-density switching systems
facing?

Alderson, Universal Switching Corp.:
We have continued to push the technical boundaries of automated switching,
and one of the keys to doing this is to keep
abreast of the continuous component
development and integrate this into the
current product offering. This manifests
itself in the release of a new product, or an
update to an existing product to improve
performance and/or reduce costs.

Features and attributes
What key features or attributes are customers asking for in low/mid-density
switching systems?
DECEMBER 2019 EVALUATIONENGINEERING.COM

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Evaluation Engineering

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