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Analyzing Device Power Consumption Using
a 2280S Precision Measurement Supply
Application Note
As battery-powered wireless devices have become a standard Traditional ways of measuring
part of everyone's life, battery consumption becomes a critical
factor of the device's performance. More and more studies are low current
focused on improving the power efficiency of electric devices There are two traditional ways to measure low currents:
and components.
1. Connect a precision resistor, R, in series with the circuit and
For the battery-powered devices, the power consumption can measure the voltage across the resistor, VR with a high-pre-
be represented by the input current because the input voltage cision digital multimeter. Calculate the current value as VR/R.
is a constant voltage during a load current measurement. If we
2. Measure the current by using an oscilloscope and a cur-
can measure the load current under different working modes,
rent probe.
we will be able to compute power consumption. As a result,
we will be able to deduct the device's battery life in its active However, both ways have limitations.
modes and its standby mode. However, measuring DC current
precisely, especially low current can be a difficult challenge. Measuring current with a digital
Accurately measuring the load current down to milliamp or mulitimeter
even to microamp levels without affecting the original circuit
To measure the current with a precision sense resistor in
current presents significant challenges for the test methodol-
series, the engineer has broken the circuit and inserts a resis-
ogy used and for the selection of appropriate instrumentation
tor in a location which will not compromise the resistance with
with sufficient sensitivity.
components that would be in parallel with the sense resistor.
Application Note
For low current measurement, a resistor with resistance of at A wireless device will transition near-instantaneously to its full
least 1 and a high-precision voltage measurement device power mode during the device's RF transmission state. When
must be chosen. This technique adds a number of error terms. the device's load current changes from a low standby current
If a resistor with 1% tolerance is used, a measurement error of 10