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Current Drain Analysis Enhances
WLAN Network Card Design and Test
Application Note 1468
The trend is clear. Wireless
Local Area Networks (WLANs)
are quickly supplanting conven-
tional LAN connections. Newer
WLAN standards with improved
interoperability and greater data
rates are rapidly being developed
and deployed. Critical to the
success of new laptop WLAN
network cards is minimizing
their current drain. Their high
power demand can reduce the
battery operating time of their
host laptop or notebook PC as
much as 50%. Considerable effort
is being made on reducing
power consumption of WLAN
network cards, from further
integration at the silicon level
to enhanced power management
at the Medium Access Control
(MAC) layer. These efforts all
measurements, analyzing the
start with having effective means
dynamics of the current drain
for measuring and evaluating
signal provides valuable insight
the current drain of designs in
to the WLAN card's behavior
their various operating modes
and on optimizing its operation.
and assessing the impact of
Accurately making these DC
subsequent design improve-
and dynamic current measure-
ments. Going beyond basic
ments can turn out to be quite
challenging in practice.
Agilent Technologies
Agilent DC sources and application software simplify
measurement and analysis of current drain consumption
on WLAN network cards
The Agilent 66319B and Key Operating States and Modes There are various power
66321B DC Sources have for Current Drain Measurements savings settings that can be
specialized capabilities suited WLAN network cards typically selected, such as:
for powering and measuring feature multiple operating 1.Power savings-off (always
the current drain on WLAN states to enhance their perfor- active mode) setting
network cards during test, mance as a networked device, 2.Normal power savings-on
whether for R&D, design while still minimizing power (doze mode) setting
verification, or manufacturing. consumption.
The Agilent 14565B Device 3.Maximum power savings-on
(deeper doze mode) setting
Characterization Software As a minimum the operating
captures, analyzes, and states include:
The power savings-off setting
visualizes dynamic current 1 Active/transmit state provides the fastest level of
drain activity over long periods,
2.Active/receive state response, as all sub circuits
making it ideal for evaluating
3.Sleep state(s) on the WLAN card are always
and optimizing power
active. Operation switches back
consumption of WLAN
These operating states each and forth between transmit
network cards in R&D and
have a specific level of activity and receive states as needed.
verification testing.
with a corresponding level of Depending on the power
power consumption. There may savings-on setting selected,
This application note
be several sleep states having the MAC will switch the WLAN
demonstrates how these products
different power levels with card into, and have it spend a
can be applied to simplify the
corresponding wake up times. portion of its time in a sleep
complex task of accurately
The MAC determines the state state, periodically switching
measuring and evaluating the
of operation. The DC current back to the active states to
current drain of a WLAN
drain for each of these states check for messages. Deeper
network card for its various
is a good indicator of correct dose mode shuts more of the
operating modes, in this case
operation and hence, is useful card's circuits down and takes
an 802.11a WLAN card.
to measure, whether for R&D, longer to wake up again. When
verification, or manufacturing awakened, the WLAN card will
test. These states, however, remain active until it is told it
being under control of the is no longer needed.
MAC, are not typically directly
selectable, making it difficult The relative amount of time
to measure their respective the WLAN card remains in
current drains. each of its various states
depends on the use activity
and MAC power management
design. Good use models need
to account for extremely random
use nature. Developing more
effective power management
2
algorithms requires running Powering the WLAN card allows PCMCIA I/O cards to be
representative long-term use directly with the 66319B DC swapped out while the laptop
models while measuring the source has some advantages: is on. It is important that Vcc
corresponding current drain