CC2400_07 Datasheet, PDF (54/83 Pages) Texas Instruments – 2.4 GHz Low-Power RF Transceiver

CC2400
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 28 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 be 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 on 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 to
disconnect the PA in RX mode. See
Figure 29.
SWRS042A
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