CC2500_06 Datasheet, PDF (50/84 Pages) Texas Instruments – Single Chip Low Cost Low Power RF Transceiver

CC2500
FREQEST status register as described in
Section 14.1. The measured frequency offset
can be used to calibrate the frequency using
the ‘external’ transmitter as the reference. That
is, the received signal of the device will match
the receiver’s channel filter better. In the same
way the centre frequency of the transmitted
signal will match the ‘external’ transmitter’s
signal.
30.7 Spectrum Efficient Modulation
CC2500 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.
30.8 Low Cost Systems
As the CC2500 provides 500 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
Antenna
achieved in the antenna topology, see Figure
3.
A HC-49 type SMD crystal is used in the
CC2500EM reference design. Note that the
crystal package strongly influences the price.
In a size constrained PCB design a smaller,
but more expensive, crystal may be used.
30.9 Battery Operated Systems
In low power applications, the SLEEP state
with the crystal oscillator core switched off
should be used when the CC2500 is not active.
It is possible to leave the crystal oscillator core
running in the SLEEP state if start-up time is
critical.
The WOR functionality should be used in low
power applications.
30.10 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 28.
Filter
PA
Balun
CC2500
T/R switch
T/R switch
Figure 28. Block diagram of CC2500 usage with external power amplifier
PRELIMINARY Data Sheet (Rev.1.2) SWRS040A
Page 50 of 83