CC400-RTR2 datasheet(19/31 Pages) TI

19 / 31 page

CC400

SWRS050

Page 19 of 32

24.

PLL Lock Indicator

The

CC400 PLL lock indicator is available

on the LOCK pin. The PLL lock signal is

not 100% conclusive. That is, if the LOCK

signal indicates lock (i.e. a high signal on

the LOCK pin) the PLL has locked to the

desired frequency. However, situations

might arise where the lock signal does not

indicate lock (i.e. a low signal on the

LOCK pin) when in fact the PLL has

locked to the desired frequency.

25.

Antenna Considerations

The

CC400 can be used together with

various types of antennas. The most

common

antennas

for

short-range

communication are monopole, helical and

loop antennas.

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 integrated into the PCB.

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.

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. But helical

antennas tend to be more difficult to

optimise 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

λ/4-

monopole antenna is recommended giving

the best range and because of its

simplicity.

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 433.92 MHz should be

16.4 cm.

The antenna should be connected as

close as possible to the IC. If the antenna

is located away from the input pin the

antenna should be matched to the feeding

transmission line. See Application Note

AN003 “Antennas” for more details.

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