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off some measurement accuracy and
resolution to get speed.
Figure 1 illustrates a typical load
current profile for a wireless IoT
device. In sleep mode, the current
is very low, but when the device is
transmitting, the load current rises
dramatically for a short period.
To measure this current, the test
instrumentation must respond to
control signals that indicate when the
device is transitioning into the active
state so that the instrumentation can
initiate the high-speed measurement.
The instrument should also allow
flexibility in selecting a measurement
time so that the best measurement
can be acquired.
Because the requirements for making
accurate low current measurements
during sleep and standby modes and
those for making very fast high current
measurements during the active mode
are so different, one might assume
that multiple instruments would be
required tomake thesemeasurements.
For example, it would be possible to
put a sense resistor in series with the
test lead that connects a power supply
to the device-under-test and measure
the voltage across the sense resistor
with a digital multimeter (DMM).
However, it would be very challenging
to choose the appropriate value for the
sense resistor. A small resistor value
adds only a small additional error to
the load current measurement, but if
the value is too small, the DMM might
lack sufficient sensitivity to measure
the low sleep mode current, or even
the standby mode current, accurately.
Although an oscilloscope is well suited
to the task of capturing the magnitude
of short, active-mode load current
Figure 1. The load current profile for a typical wireless device includes long periods of low current consumption with short
bursts of high current consumption when the device is stimulating or transmitting data
Figure 1. The load current profile for a typical wireless device includes long periods
of low current consumption with short bursts of high current consumption when
the device is stimulating or transmitting data.
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