CC2480_11 Datasheet, PDF (35/48 Pages) Texas Instruments – Z-Accel 2.4 GHz ZigBee Processor

CC2480
10.12 PCB Layout Recommendation
In the Texas Instruments reference design, the
top layer is used for signal routing, and the
open areas are filled with metallization
connected to ground using several vias. The
area under the chip is used for grounding and
must be well connected to the ground plane
with several vias.
The ground pins should be connected to
ground as close as possible to the package
pin using individual vias. The de-coupling
capacitors should also be placed as close as
possible to the supply pins and connected to
the ground plane by separate vias. Supply
power filtering is very important.
10.13 Antenna Considerations
CC2480 can be used together with various
types of antennas. A differential antenna like a
dipole would be the easiest to interface not
needing a balun (balanced to un-balanced
transformation network).
The length of the λ/2-dipole antenna is given
by:
L = 14250 / f
where f is in MHz, giving the length in cm. An
antenna for 2450 MHz should be 5.8 cm. Each
arm is therefore 2.9 cm.
Other commonly used antennas for short-
range communication are monopole, helical
and loop antennas. The single-ended
monopole and helical would require a balun
network between the differential output and
the antenna.
Monopole antennas are resonant antennas
with a length corresponding to one quarter of
the electrical wavelength (λ/4). They are very
easy to design and can be implemented
simply as a “piece of wire” or even integrated
into the PCB.
The length of the λ/4-monopole antenna is
given by:
L = 7125 / f
where f is in MHz, giving the length in cm. An
antenna for 2450 MHz should be 2.9 cm.
Non-resonant monopole antennas shorter than
λ/4 can also be used, but at the expense of
range. In size and cost critical applications
such an antenna may very well be integrated
into the PCB.
Enclosing the antenna in high dielectric
constant material reduces the overall size of
The external components should be as small
as possible (0402 is recommended) and
surface mount devices must be used.
If using any external high-speed digital
devices, caution should be used when placing
these in order to avoid interference with the
RF circuitry.
It is strongly advised that this reference layout
is followed very closely in order to obtain the
best performance.
The schematic, BOM and layout Gerber files
for the reference designs are all available from
the TI website.
the antenna. Many vendors offer such
antennas intended for PCB mounting.
Helical antennas can be thought of as a
combination of a monopole and a loop
antenna. They are a good compromise in size
critical applications. Helical antennas tend to
be more difficult to optimize than the simple
monopole.
Loop antennas are easy to integrate into the
PCB, but are less effective due to difficult
impedance matching because of their very low
radiation resistance.
For low power applications the differential
antenna is recommended giving the best
range and because of its simplicity.
The antenna should be connected as close as
possible to the IC. If the antenna is located
away from the RF pins the antenna should be
matched to the feeding transmission line
(50Ω).
CC2480 Data Sheet SWRS074
Page 35 of 43