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It has been predicted that, within a
decade, the Internet of Things (IoT)
will grow to encompass billions or
even trillions of wireless devices
and sensors. However, that growth
will depend to some degree on the
ability of their manufacturers to
drive down the cost of each of these
devices. At the same time, however,
these devices must be thoroughly
characterized during their design and
development, then tested quickly,
accurately, and cost-effectively during
production. To operate reliably for
extended periods on a finite amount
of battery power, these tiny wireless
devices must consume power
sparingly. This requires characterizing
a device’s power consumption in all
of its operating states so developers
can understand where to focus their
efforts.
Characterizing the power consumption
of
these
devices
demands
instrumentation capable of making
both sensitive measurements and high
speed measurement. For example,
when characterizing load currents,
the test system must be capable of
measuring low currents, sometimes
down to tens of microamps or less,
when the device is in its sleep and
standby modes. To produce stable
and accurate measurements of these
low-level currents, test systems
are generally configured to make
many measurements over a long
measurement interval in order to
average out electrical noise created in
the device and noise from the external
environment. Filtering can also be
used to ensure quality measurements.
However, a measurement period that
extends over a number of AC power
line cycles along with filtering can
result in a measurement time well
into the seconds and often tens of
seconds. This extended measurement
period runs in opposition to the need
for high speed to increase throughput
and reduce the cost of test for each
part.
In addition to making slow, sensitive
measurements of the sleep or
standby currents of IoT devices, the
instrumentation must make very
fast current measurements when an
IoT device is active, such as when it
is transmitting data. The challenge
is to capture and measure a load
current pulse that might last for only
a few hundred microseconds. The
instrumentation must respond quickly
to make a measurement in this very
short time interval. In this situation,
the test system designer must trade
Fast, Accurate, Economical Testing of Low-
Power Devices Will Be Crucial to the Growth of
the Internet of Things
Robert Green, Keithley Instruments, a Tektronix Company
58 l New-Tech Magazine Europe