Low Power Wireless
That leads us to the other means to
improve the range of our wireless design.
MORE POWER
Outside of any improvements to the
antennas, additional signal power from
the transmitter will always provide better
range. In a purely theoretical situation,
again using the Maxim Link Budget
Calculator as a guide7, it is easy to show
that an additional 3 dB of transmitter
power results in 30~40m of additional
range. This range improvement drops to
about 20m when including a perfect flatground
reflection. For every 3 dB of extra
output power at the transmitter, a system
designer can often achieve an additional
20~30m of range in the real world.
Unfortunately, this extra power can be
hard to find as an integrated option. Upon
finding a more powerful integrated transmitter,
there is usually a noticeable supply
current penalty to be paid in addition to a
higher material cost (i.e., a more expensive
IC). Often, the higher output power is
not obtained through increased efficiency,
but rather, the integrated circuit often has
increased the power consumption (voltage
and/or current) from the PA supplies.
When this power source is a simple coincell
battery, the higher transmitter power
almost always means shorter lifetime for
the system.
On the other side of the wireless link is
the receiver.
BETTER SENSITIVITY
Just like producing more output power
at the transmitter, a receiver IC with
improved sensitivity levels equates to an
enhancement in range. 3-dB of improvement,
this time with lower sensitivity,
could help the system reach another
20~30m. As with increased transmitter
power, better receiver sensitivity almost
always comes with additional supply
current and a higher IC cost. Fortunately,
the receivers used in wireless systems
tend to be connected to line-power, so
the power budget penalty may not be as
severe. However, the cost premium for
a modest improvement in sensitivity can
still be notable—over 30% for just 3 dB
better sensitivity8.
The sweet spot for the best increase
in range with the fewest penalties from
design tradeoffs (time, BOM cost, system
budgets, etc.) turns out to be a higher
power transmitter.
MAXIM’S NEW TRANSMITTERS
Because we perceived a need in the
market, Maxim developed a new family of
transmitters to help SRD system designers
reach farther with no penalty
to other budgets.
The MAX4146x is a
new, high-output power,
low-current transmitter
capable of up to +16 dBm
of transmitted power
while still running on a
3-V coin-cell battery.
The family achieves this
while keeping the supply
current in familiar territory
such as <9 mA in ASK
modulation (434 MHz,
3.0 V) and 15 mA for FSK
modulation (434 MHz,
3 V), even though they
produce an impressive
+13 dBm of output power
(typical, 300~450 MHz, including
matching/filtering)
with little to no impact on
the power budget. The
family is also capable of
over +16 dBm of output
with a high-power match
or using “Boost Mode”
within an industry-leading
current of <26 mA.
These new transmitters
allow the RF
Figure 1 – Voyager and SRD link budgets.
engineer to design-in more than 20m of
extra range without any penalty to their
traditional battery-powered system. By
using an optimized high-power matching
and/or Boost Mode, the SRD system
designer could add as much as 60m
of range simply by choosing the new
MAX4146x transmitter. This demonstrates
that you do not need to be a rocket
scientist to “maximize” your range!
REFERENCES
1 MAX41464/63 Data Sheet, https://
www.maximintegrated.com/en/ds/
MAX41463-MAX41464.pdf, Jun 2018
2 Application Note 5142 – Radio
Link-Budget Calculations for ISM-RF
Products, https://www.maximintegrated.
com/en/app-notes/index.mvp/
id/5142, Martin Stoehr, 2 Nov 2011
3 Elektronik Magazine article
“Kurzstrecken-Funksysteme professionell
entwickeln” (English title:
“Getting Started with a Radio Design”),
“Article of the Year” for 2013,
http://www.elektroniknet.de/elektronik/
halbleiter/die-elektronik-autoren-desjahres
2013-107374-Seite-4.html
4 Application Note 3586 – Path Loss
in Remote Keyless Entry Systems,
https://www.maximintegrated.com/en/
app-notes/index.mvp/id/3945, Larry
Burgess, 19 Jul 2005
5 DESCANSO Design and Performance
Summary Series | Article 4 | Voyager
Telecommunications, https://descanso.
jpl.nasa.gov/DPSummary/Descanso4
Voyager_new.pdf, Roger Ludwig
and Jim Taylor, March 2002
6 Voyager 1 Link Budget Calculations,
“ISM-RF Link Budget A06 – Voyager1.
xlsx”, Oct 2018
7 SRD Link Budget Calculations, “ISMRF
Link Budget A06 – SRD System.
xlsx”, Oct 2018
8 Price comparison for Si4356 at
-113dBm for $1.26, versus Si4355 at
-116dBm for $1.48 (~17.5% increase),
or Si4455 at -116dBm for $1.66
(~31.7% increase); https://www.silabs.
com/products/wireless/proprietary/
ezradio-ism-band-transmitters-recievers
transceivers, 7 Nov 2018
ABOUT THE AUTHOR
Martin D. Stoehr has been working in
the analog and mixed-signal IC industry
since graduating from the University of
Colorado in 1994 with a BSEE in communication
systems and control theory. For
the past 18 years he has been designing
various board-level systems at Maxim
Integrated, from fully automated bench
test systems to characterization boards,
evaluation kits, reference designs, and
demonstrators.
www.mwee.com March - April 2019 MW 21
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/die-elektronik-autoren-desjahres-2013-107374-Seite-4.html
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/www.mwee.com
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/Descanso4--Voyager_new.pdf