CC2430 Datasheet, PDF (188/234 Pages) Texas Instruments – A True System-on-Chip solution for 2.4 GHz IEEE 802.15.4 / ZigBee-TM

CC2430
data to chip data. Remember that
the chip sequence transmitted by
the test setup is not the same as
the bit sequence, which is output
by CC2430.
• When operating at or below the
sensitivity limit, CC2430 may lose
symbol synchronization in infinite
receive mode. A new SFD and
restart of the receiver may be
required
to
re-gain
synchronization.
In an IEEE 802.15.4 system, all
communication is based on packets. The
sensitivity limit specified by [1] is based on
Packet Error Rate (PER) measurements
instead of BER. This is a more realistic
measurement of the true RF performance
since it mirrors the way the actual system
operates.
Chipcon recommends performing PER
measurements instead of BER
measurements to evaluate the
performance of IEEE 802.15.4 systems.
To do PER measurements, the following
may be used as a guideline:
• A valid preamble, SFD and length
field must be used for each
packet.
• The PSDU (see Figure 45 on
page 173) length should be 20
bytes for sensitivity measurements
as specified by [1].
• The sensitivity limit specified by [1]
is the RF level resulting in a 1%
PER. The packet sample space
for a given measurement must
then be >> 100 to have a
sufficiently large sample space.
E.g. at least 1000 packets should
be used to measure the
sensitivity.
14.32 PCB Layout Recommendation
A two layer PCB is highly recommended.
In Chipcon’s 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 data transmitted over air must
be spread according to [1] and the
description on page 165. Pre-
generated packets may be used,
although [1] requires that the PER
is averaged over random PSDU
data.
• The CC2430 receive FIFO may be
used to buffer data received
during PER measurements, since
it is able to buffer up to 128 bytes.
• The
MDMCTRL1H.CORR_THR
control register should be set to
20, as described in the
Demodulator,
Symbol
Synchronizer and Data Decision
section.
The simplest way of making a PER
measurement will be to use another
CC2430 as the reference transmitter.
However, this makes it difficult to measure
the exact receiver performance.
Using a signal generator, this may either
be set up as O-QPSK with half-sine
shaping or as MSK. If using O-QPSK, the
phases must be selected according to [1].
If using MSK, the chip sequence must be
modified such that the modulated MSK
signal has the same phase shifts as the O-
QPSK sequence previously defined.
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 42
on page 165. 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:
(c₀ xnor c₁), (c₁ xor c₂), (c₂ xnor c₃), … ,
(c_32n-1 xor c_32n) where c_32n may be
arbitrarily selected.
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.
CC2430 PRELIMINARY Data Sheet (rev. 1.03) SWRS036A
Page 188 of 232