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Keysight Technologies
New Probing Technology Enables
High Sensitivity, Wide Dynamic
Range Current Measurement
Application Note
Introduction
As modern battery-powered devices and integrated circuits become more
green and energy efficient, there is a growing need to make high sensitiv-
ity, low level current measurements to ensure these devices' current
consumption is within acceptable limits. The key applications calling for
accurate power consumption measurement are battery-powered applica-
tions such as wireless mobile devices and consumer electronics. To maxi-
mize the battery life, engineers need to minimize the power consumption
over the life of the product. Power is defined as P = V x I. The key enabler
of reducing the power consumption of a device is to lower the average
current consumption for a fixed supply voltage level.
A primary challenge in measuring the current consumption of battery-
powered mobile devices, such as a cell phone or a tablet computer, is
that the dynamic range of the current signal is very wide. The mobile
device typically switches back and forth between active states, where it
draws very high and fast peak currents, and an idle or standby current
mode, where it draws very small DC and AC currents.
Figure 1 shows the current drain measured on a GSM cell phone when
making a call. The active current peaks as high as ~2 A, and at idle
mode, the current drain is extremely small.
Figure 1 The current drain measured on a GSM cell phone when making a call.
02
A simple way to measure a current with an oscilloscope is to use a clamp-on type
current probe such as the Keysight Technologies, Inc. 1147B or N2893A to directly
monitor the current going into the device.
Unfortunately, this approach is not appropriate for measuring small currents that
rapidly change between sub-milli amps and several amps because of the limited
dynamic range and sensitivity of the clamp-on type current probe, which is limited
to a few milli amps. In the example for measuring the current consumption of a
mobile phone, the idle state current is not quite measurable because it is buried in
the probe noise.
Also, for a more accurate measurement, one would occasionally degauss the probe
to remove residual magnetism from the probe core and compensate for any DC
offset of the clamp-on current probe. This extra calibration procedure makes the
clamp-on current probe cumbersome to use.
Figure 2 A simple way to measure a current with an oscilloscope is to use a clamp-on type
current probe such as Keysight's 1147B or N2893A.
The new N2820A Series high-sensitivity current probes from Keysight Technologies
address the need for high-sensitivity current measurements with a wide dynamic
range. These probes also offer the advantage of physically small connections to the
device under test (DUT) since today's application environments require an extremely
small form factor. The new N2820A/21A AC/DC current probes offer the industry's
highest sensitivity among oscilloscope current probes, going all the way down to 50
uA with a maximum current range of 5 A.
03
Keysight's N2820A 2-channel high sensitivity current probe comes with two par-
allel differential amplifiers inside the probe with different gain settings, where
the low gain side allows you to see the entire waveform or the "zoom out"
view of the waveform and the high gain amplifier provides a "zoom in" view
to observe extremely small current fluctuations, such as a mobile phone's idle
state. The N2820A/21A current probes are optimized for measuring the current
flow within the DUT to characterize sub-circuits, allowing the user to see both
large signals and details on fast and wide-dynamic current waveforms.
Figure 3 The new N2820A/21A AC/DC current probes offer the industry's highest
sensitivity among oscilloscope current probes.
The probe offers an innovative method of connecting the probe to your DUT.
The supplied Make-Before-Break (MBB) connectors allow you to quickly probe
multiple locations on your DUT without having to solder or unsolder the leads.
The MBB header may be mounted on your target board or wired out of the DUT.
It fits into standard 0.1" spacing thru-holes for 0.025" square pins. Users should
plan their PCB layouts accordingly. The MBBs are a great way to easily connect
and disconnect across multiple locations on the target board without interrupt-
ing the circuit under test.
Figure 4 The supplied Make-Before-
Break (MBB) connectors allow you
to quickly probe multiple locations
on your DUT without having to
solder or unsolder the leads.
04
The innovation hasn't stopped there. With current waveforms captured, you
now want to calculate the average current consumption of the system over
time. Keysight's Infiniium and InfiniiVision oscilloscopes provide an area under
the curve measurement (Charge), where you can easily calculate the integrated
current consumptions in Ah (Ampere x Hour) over time. The `Ah' is a unit of
measurement of a battery's electrical storage capacity. One Ah is equal to a
current of one ampere flowing for one hour.
Now with the N2820A/21A current probes, engineers in battery-powered prod-
uct testing are able to see the details and the big picture on dynamic current
waveforms like never before with traditional clamp on probes.
Figure 5 Keysight's Infiniium and InfiniiVision oscilloscopes provide an area under the
curve measurement (Charge), where you can easily calculate the integrated current
consumptions in Ah (Ampere x Hour) over time.
05
06 | Keysight | Make High Sensitivity, Wide Dynamic Range Current Measurement - Application Note
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