CC2420-RTR1 datasheet(59/92 Pages) TI

59 / 92 page

CC2420

SWRS041B

Page 59 of 89

•

The

RXCTRL1.RXBPF_LOCUR

control bit should be set to 1.

The simplest way of making a PER

measurement will be to use another

CC2420 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, … ,

sn-1 of length n symbols, the desired chip

sequence c0, c1, c2, …, c32n-1 of length 32n

is found using table lookup from Table 3

on page 24. 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), … ,

(c32n-1 xor c32n) where c32n may be

arbitrarily selected.

35 PCB Layout Recommendations

Following Texas Instruments’s reference

design is highly recommended.

In our reference design, the top layer is

used for signal routing, and the open

areas

are

filled

with

metallisation

connected to ground using several vias.

Layer 2 has not been used in our CC2420

reference designs. Layer 3 is used for

power routing and the bottom layer serves

as ground plane with a little routing.

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.

Caution should be used when placing the

microcontroller

order

avoid

interference with the RF circuitry.

A Development Kit with a fully assembled

Evaluation Module is available. It is

strongly advised that this reference layout

is followed very closely in order to get the

best performance.

The schematic, BOM and layout Gerber

files for the reference designs are all

available from the Texas Instruments

website.

36 Antenna Considerations

CC2420 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

CC2420-RTR1 数据表(PDF) 59 Page - Texas Instruments

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