CC2400_08 Datasheet, PDF (38/84 Pages) Texas Instruments – 2.4 GHz Low-Power RF Transceiver

CC2400
27 FSK Modulation Formats
The data modulator can modulate 2FSK,
which is two level FSK, and GFSK, which
is a Gaussian filtered FSK with BT=0.5 at
1 Mbps (for lower data rates BT will be
higher).
The purpose of the GFSK is to make a
more bandwidth efficient system. The
modulation and the Gaussian filtering is
performed
internally.
The
GRMDM.TX_GAUSSIAN_FILTER
bit
enables the GFSK.
However, if GFSK modulation is used
together with a data rate of 1 Mbps, it is
recommended to use a preamble length of
32 bytes as otherwise packet error
performance can be affected.
Figure 18 shows a plot of the spectrum for
FSK and GFSK modulation. Input data
was a PN9 sequence. The plot was
captured using a spectrum analyzer set to
5 MHz span and 300 kHz RBW.
0
-10
-20
-30
FSK
GFSK
-40
-50
-60
-70
2,438
2,439
2,440
2,441
Frequency [GHz]
2,442
2,443
Figure 18. Modulated spectrum
28 Built-in Test Pattern Generator
The CC2400 has a built-in test pattern
generator that can generate a PN9
pseudo random sequence. The
MDMTST0.TX_PRNG bit enables the PN9
generator.
The PN9 pseudo random sequence is
defined by the polynomial x⁹ + x⁵ + 1.
The PN9 generator can be used for
transmission of ‘real-life’ data when
measuring modulation bandwidth or
occupied bandwidth.
SWRS042A
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