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CC112X/CC1175
SWRU295C
Page 30 of 108
5
Receive Configuration
5.1
RX Filter Bandwidth
In order to meet different channel width requirements, the RX filter BW is programmable. The
register fields control the RX filter
register field and the crystal oscillator frequency. It
is recommended to use SmartRF Studio to generate settings for a given RX filter BW.
Equation 10 and Equation 11 give the relation between the register settings and the channel filter
bandwidth.
8
_
_
BW
Filter
RX
DECFACT
CIC
BB
Factor
Decimation
f
xosc
Equation 10: RX Filter BW (
CHFILT_BYPASS = 0
)
2
_
_
BW
Filter
RX
DECFACT
CIC
BB
Factor
Decimation
f
xosc
Equation 11: RX Filter BW (
CHFILT_BYPASS = 1
)
The decimation Factor is 20 when
and 32 when
.
Table 16 and Table 17 list some channel filter bandwidths configurations supported by the
CC112X
.
ADC_CIC_DECFACT = 0
ADC_CIC_DECFACT = 1
BB_CIC_DECFACT
RX Filter BW [kHz]
BB_CIC_DECFACT
RX Filter BW [kHz]
0x01
250
0x01
156
0x03
83
0x02
78
0x05
50
0x03
52
0x0A
25
0x06
26
0x14
12.5
0x0D
12
0x28
6.25
0x19
6.25
Table 16: RX Filter BW with f
XOSC
= 40 MHz (CC1125) and
CHFILT_BYPASS = 0
ADC_CIC_DECFACT = 0
ADC_CIC_DECFACT = 1
BB_CIC_DECFACT
RX Filter BW [kHz]
BB_CIC_DECFACT
RX Filter BW [kHz]
0x01
200
0x01
125
0x02
100
0x02
62.5
0x04
50
0x03
42
0x08
25
0x05
25
0x10
12.5
0x0A
12
Table 17: RX Filter BW with f
XOSC
= 32 MHz (CC1120 and CC1125) and
CHFILT_BYPASS = 0
By compensating for a frequency offset between the transmitter and the receiver, the filter bandwidth
can be reduced and the sensitivity can be improved. The RX filter BW must at least be twice the
symbol rate. A narrow bandwidth gives better sensitivity and selectivity at the cost of more accurate
RF crystals.
sets the bandwidth into the digital low-IF mixer.
If the selected RX filter bandwidth is large compared to the symbol rate (10 times of more), sensitivity
can be improved by setting
.