CC2430 Datasheet, PDF (175/212 Pages) Texas Instruments – A True System-on-Chip solution for 2.4 GHz IEEE 802.15.4 / ZigBee-TM

CC2430
Radio : PCB Layout Recommendation
chip sequence must be modified such that the
modulated MSK signal has the same phase
shifts as the O-QPSK sequence previously
defined.
page 154. It can be seen from comparing the
phase shifts of the O-QPSK signal with the
frequency of a MSK signal that the MSK chip
sequence is generated as:
For a desired symbol sequence s₀, s₁, … , s_n-1
of length n symbols, the desired chip
sequence c₀, c₁, c₂, …, c_32n-1 of length 32n is
found using table lookup from Table 44 on
(c₀ xnor c₁), (c₁ xor c₂), (c₂ xnor
c₃), … , (c_32n-1 xor c_32n)
where c_32n may be arbitrarily selected.
14.32 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.
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.
A Development Kit, CC2430DK, with a fully
assembled Evaluation Module is available. 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.
14.33 Antenna Considerations
CC2430 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 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.
CC2430 Data Sheet (rev. 2.1) SWRS036F
Page 175 of 211