CC2420-RTR1 datasheet(58/92 Pages) TI

58 / 92 page

CC2420

SWRS041B

Page 58 of 89

34.6

Low-cost systems

As the

CC2420 provides 250 kbps multi-

channel performance without any external

filters, a very low-cost system can be

made.

A differential antenna will eliminate the

need for a balun, and the DC biasing can

be achieved in the antenna topology.

34.7

Battery operated systems

In low power applications, the

CC2420

should be powered down when not being

active. Extremely low power consumption

may be achieved when disabling also the

voltage

regulator.

This

will

require

reprogramming of the register and RAM

configuration.

34.8

BER / PER measurements

CC2420 includes test modes where data is

received infinitely and output to pins

(RX_MODE 2, see page 40). This mode

may be used for Bit Error Rate (BER)

measurements. However, the following

actions must be taken to do such a

measurement:

•

A preamble and SFD sequence

must be used, even if pseudo

random data is transmitted, since

receiving the DSSS modulated

signal

requires

symbol

synchronisation,

not

bit

synchronisation like e.g. in 2FSK

systems. The SYNCWORD may be

set to another value to fit to the

measurement setup if necessary.

•

The data transmitted over air must

be spread according to [1] and the

description on page 24. This

means that the transmitter used

during measurements must be

able to do spreading of the bit

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

CC2420.

•

When operating at or below the

sensitivity limit,

CC2420 may loose

symbol synchronisation in infinite

receive mode. A new SFD and

restart of the receiver may be

required

re-gain

synchronisation.

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 accurate

measurement of the true RF performance

since it mirrors the way the actual system

operates.

It is recommended to perform PER

measurements

instead

BER

measurements

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 17 on

page 36) 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

used

measure

the

sensitivity.

•

The data transmitted over air must

be spread according to [1] and the

description on page 24. Pre-

generated packets may be used,

although [1] requires that the PER

is averaged over random PSDU

data.

•

The

CC2420 receive FIFO may be

used to buffer data received

during PER measurements, since

it is able to buffer up to 128 bytes.

•

The

MDMCTRL1.CORR_THR

control register is by default set to

20,

described

the

Demodulator,

Symbol

Synchroniser and Data Decision

section.

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