Evaluation Engineering - 17

AUTOMATED TEST

WHAT'S ALL THIS TALK
ABOUT DENSITY?
When it comes to switching in functional test, density is key.
In this article, let's examine some of the reasons why.
By Bob Stasonis
	

In the world of test, smaller is better,
provided the system can test my particular devices under test (DUTs). There
are many reasons to look at smaller footprints in test-manufacturing floor space,
shorter cable lengths, and portability
come to mind.
In the world of signal switching and
test, the word is not necessarily smaller,
but denser. Switching density is always a
subject for debate as to how much switching is necessary, particularly in modular
test systems because of the fixed physical size of modular devices. In this short
article, we will take a brief look at some of
the advantages of high-density switching
and some sample applications that benefit
from it. For brevity's sake, this article will
focus on crosspoint matrices. The purpose
of a crosspoint matrix is to allow any
number of multiple signal inputs to be
connected to any number of signal outputs-basically any test resource to any
test point on one or more DUTs. A 1-wire
crosspoint matrix uses an array of SPST
relays to close an X to Y path. In Figure
1, with path Y1 to X1 closed (green path,
right image), a stub appears (red) on the
line which limits the matrix bandwidth.

Advantages of density
Loosely defined, switching density is the
number of relays that can fit into a unit of
measure such as a test-system 19-in. rack
unit or a modular instrumentation platform slot. For example, in the PXI modular
format, 544 relays can be accommodated
in a single-slot matrix module. However,
using an architecture such as Pickering's

Figure 1: Crosspoint matrix, with green showing path Y1 to X1 closed and red showing a stub, which
limits bandwidth.

Figure 2: PXI ultrahigh-density BRIC matrix
(left), shown with PXI high-density precision
resistor module (right).

BRIC, higher slot densities can be achieved,
with up to 768 relays per slot (Figure 2).
To achieve the high densities, the relays
must be physically small, with a 0.5-A
maximum limit, usable for many small-

signal applications.
Modules that can
switch higher current
signals will require physically larger relays,
and the resulting density per PXI slot will
go down. But the critical point here is that
thanks to the advancement in relay technology, switching density has dramatically
improved in the past 10 years. This means
FEBRUARY 2020 EVALUATIONENGINEERING.COM

17



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Evaluation Engineering

Table of Contents for the Digital Edition of Evaluation Engineering

Editor's Note: Oscilloscope features and specs evolve to match engineers' environment
By the Numbers
Industry Report
Oscilloscopes: Innovation drives scope options
Aerospace: From the simulation environment to the flightline
Automated Test: What's all this talk about density?
Inspection: New manufacturing processes inspired by flex
Software: Meeting 5G challenges from code generation to spectrum congestion
Tech Focus
Featured Tech
Evaluation Engineering - Cover1
Evaluation Engineering - Cover2
Evaluation Engineering - 1
Evaluation Engineering - By the Numbers
Evaluation Engineering - 3
Evaluation Engineering - Industry Report
Evaluation Engineering - 5
Evaluation Engineering - Oscilloscopes: Innovation drives scope options
Evaluation Engineering - 7
Evaluation Engineering - 8
Evaluation Engineering - 9
Evaluation Engineering - Aerospace: From the simulation environment to the flightline
Evaluation Engineering - 11
Evaluation Engineering - 12
Evaluation Engineering - 13
Evaluation Engineering - 14
Evaluation Engineering - 15
Evaluation Engineering - 16
Evaluation Engineering - Automated Test: What's all this talk about density?
Evaluation Engineering - 18
Evaluation Engineering - 19
Evaluation Engineering - Inspection: New manufacturing processes inspired by flex
Evaluation Engineering - 21
Evaluation Engineering - Software: Meeting 5G challenges from code generation to spectrum congestion
Evaluation Engineering - 23
Evaluation Engineering - 24
Evaluation Engineering - 25
Evaluation Engineering - Tech Focus
Evaluation Engineering - 27
Evaluation Engineering - Featured Tech
Evaluation Engineering - 29
Evaluation Engineering - 30
Evaluation Engineering - 31
Evaluation Engineering - 32
Evaluation Engineering - Cover3
Evaluation Engineering - Cover4
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