Everyone wants longer battery life for their cell phone or other mobile device.
This typically leads designers to think about obtaining better batteries. Evaluating a new
battery requires validating the battery run time.
In a conventional validation, the mobile device is treated as a black box and the total run
time is directly measured until low-battery shut-down. This is very time-consuming.
A faster method is to measure current drain for a limited period and then extrapolate
run time based on the stated amp-hour capacity of the battery. However, this may result in
significant error if the actual current drain is different from the manufacturer’s test current.
Because battery technology improves very slowly,
it makes more sense to focus on getting the most from your present battery. This can be
done by analyzing the dynamic current drain that is demanded by the mobile device during typical use.
It includes testing and characterizing the
device, its sub-circuits, and the battery itself, both independently and in combination.
This detailed characterization of battery current drain will provide deeper insights
into the device’s operation so you can make design tradeoffs for optimizing run time.
If you have ever seen or measured the actual current drain from a battery of a mobile device,
you know that the current drain can be quite complex. The battery current can vary from
a few amps during transmit mode down to a few microamps during sleep or idle mode. The current
is highly dynamic, changing levels rapidly and over a very wide range. This creates a
significant measurement problem. Getting the detailed data that you need requires
digitizing the battery current drain at 50 kilo-samples per second or more over a wide
dynamic measurement range. Traditional digitizing data acquisition systems cannot meet this need
Some specialized DC sources can be used to
make this measurement by replacing the battery and accurately measuring the current demanded
by the device. These DC sources incorporate a high speed digitizing, wide dynamic range
measurement system that can accurately characterize a mobile device’s current consumption.
And since the measurement system is integrated into the DC source, you can avoid using an
external shunt resistor and the low-level measurement problems that go along with using that approach.
Agilent Technologies has a DC source designed
specifically to solve this difficult measurement task. The N6781A Source Measure Unit is tuned
for battery drain analysis. When combined with an Agilent N6705B mainframe
and 14585A software, it gives superior insight into the nature of the dynamic current drain
being demanded by the mobile device. In this example, you can see the results of
measuring the current drain of a mobile phone. On a single display, with a single measurement pass,
you can measure and see the: * Idle current level and duration
* Receive current activity * Transmit current level and duration
* Calculated Power Added Efficiency and more
The N6781A provides this measurement insight because it has: * A high sampling rate of 195 Kilo-samples per sec
* A wide dynamic measurement range from nano-amps to amps
* Seamless measurement ranging - over a wide range of currents so you don’t lose any data.
* Voltage source regulation of 700 micro-volts or better
* And programmable internal resistance, to accurately emulate your device’s battery
These measurement details give you unprecedented insights that allow you to relate device operation to battery drain.
This allows you to tune the performance of your device to optimize your battery’s run-time.
For more info, go to www.agilent.com/find/N6781.
And look for more videos in this series on optimizing battery life in mobile devices.