CC2400-RTR1 datasheet(54/83 Pages) TI

54 / 83 page

CC2400

SWRS042A

Page 54 of 83

The measured frequency offset can thus

be used to calibrate the frequency using

the ‘external’ transmitter as the reference.

See also page 42 (Automatic Frequency

Control).

Figure

shows

the

improvement that can be achieved.

This feature can also be used for

temperature compensation of the crystal if

the temperature drift curve is known and a

temperature sensor is included in the

system.

In less demanding applications, a crystal

with low temperature drift and low aging

could

used

without

further

compensation.

46.6 Spectrum efficient modulation

CC2400 also has the possibility to use

Gaussian shaped FSK (GFSK). This

spectrum-shaping

feature

improves

adjacent channel power (ACP) and

occupied bandwidth. In ‘true’ FSK systems

with

abrupt

frequency

shifting,

the

spectrum is inherently broad. By making

the frequency shift ‘softer’, the spectrum

can be made significantly narrower. Thus,

higher data rates can be transmitted in the

same bandwidth using GFSK.

46.7 Low latency systems

CC2400 is ideal for applications where

latency is critical. Unbuffered mode should

be used for lowest latency, since it takes

time to fill the FIFO buffer. The total

latency over the RF link in unbuffered

mode is around 8 s.

CC2400 can also

provide very low RX-TX switching time, as

described on page 47.

46.8 Low cost systems

As the

CC2400 provides 1 Mbps 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, see

Figure 4.

A small SMD crystal is used in the

reference design; note that the crystal

package strongly influences the price. In a

low-cost design, it may be preferable to

use a larger crystal package.

46.9 Battery operated systems

In low power applications, the power down

mode should be used when not active.

Depending

the

start-up

time

requirement, the crystal oscillator core can

be powered during power down. See page

36 for information on how effective power

management can be implemented.

46.10 Increasing output power

In some applications it may be necessary

to extend the link range. Adding an

external power amplifier is the most

effective way of doing this.

The power amplifier should be inserted

between the antenna and the balun, and

two

T/R

switches

are

needed

disconnect the PA in RX mode. See

Figure 29.

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