SX1231
ADVANCED COMMUNICATIONS & SENSING
DATASHEET
impact on the RSSI precision. The ADC output is one bit per channel. It needs to be decimated and filtered afterwards. This
ADC can also be used for temperature measurement, please refer to section 3.5.15 for more details.
The decimators decrease the sample rate of the incoming signal in order to optimize the area and power consumption of
the following receiver blocks.
3.5.5. Channel Filter
The role of the channel filter is to filter out the noise and interferers outside of the channel. Channel filtering on the SX1231
is implemented with a 16-tap Finite Impulse Response (FIR) filter, providing an outstanding Adjacent Channel Rejection
performance, even for narrowband applications.
Note to respect oversampling rules in the decimation chain of the receiver, the Bit Rate cannot be set at a higher value
than 2 times the single-side receiver bandwidth (BitRate < 2 x RxBw)
The single-side channel filter bandwidth RxBw is controlled by the parameters RxBwMant and RxBwExp in RegRxBw:
When FSK modulation is enabled:
FXOSC
RxBwMant × 2RxBwExp + 2
-----------------------------------------------------------------
RxBw =
When OOK modulation is enabled:
FXOSC
RxBwMant × 2RxBwExp + 3
-----------------------------------------------------------------
RxBw =
The following channel filter bandwidths are accessible (oscillator is mandated at 32 MHz):
Table 13 Available RxBw Settings
RxBwMant
RxBwExp
RxBw (kHz)
(binary/value) (decimal)
FSK
OOK
ModulationType=00 ModulationType=01
10b / 24
01b / 20
00b / 16
10b / 24
01b / 20
00b / 16
10b / 24
01b / 20
00b / 16
10b / 24
01b / 20
00b / 16
10b / 24
01b / 20
00b / 16
10b / 24
01b / 20
7
7
7
6
6
6
5
5
5
4
4
4
3
3
3
2
2
2.6
3.1
1.3
1.6
3.9
2.0
5.2
2.6
6.3
3.1
7.8
3.9
10.4
12.5
15.6
20.8
25.0
31.3
41.7
50.0
62.5
83.3
100.0
5.2
6.3
7.8
10.4
12.5
15.6
20.8
25.0
31.3
41.7
50.0
Rev 2 - Nov 2009
Page 25
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