sx1231h Semtech Corporation, sx1231h Datasheet - Page 27

• Manufacturer Part Number: sx1231h
• Description: Low Power Integrated Uhf Transceiver With On-chip +20dbm Pa
• Manufacturer: Semtech Corporation

3.4.7. DC Cancellation
DC cancellation is required in zero-IF architecture transceivers to remove any DC offset generated through self-reception.
It is built-in the SX1231 and its adjustable cutoff frequency fc is controlled in RegRxBw:
Table 15 Available DCC Cutoff Frequencies
The default value of DccFreq cutoff frequency is typically 4% of the RxBw (channel filter BW). The cutoff frequency of the
DCC can however be increased to slightly improve the sensitivity, under wider modulation conditions. It is advised to adjust
the DCC setting while monitoring the receiver sensitivity.
3.4.8. Complex Filter - OOK
In OOK mode the SX1231H is modified to a low-IF architecture. The IF frequency is automatically set to half the single side
bandwidth of the channel filter (F
A complex filter is implemented on the chip to attenuate the resulting image frequency by typically 30 dB.
Note
3.4.9. RSSI
The RSSI block evaluates the amount of energy available within the receiver channel bandwidth. Its resolution is 0.5 dB,
and it has a wide dynamic range to accommodate both small and large signal levels that may be present. Its acquisition
time is very short, taking only 2 bit periods. The RSSI sampling must occur during the reception of preamble in FSK, and
constant “1” reception in OOK.
Rev 1 - Oct 2011
ADVANCED COMMUNICATIONS & SENSING
this filter is automatically bypassed when receiving FSK signals (ModulationType = 00 in RegDataModul).
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IF
= 0.5 x RxBw). The Local Oscillator is automatically offset by the IF in the OOK receiver.
in RegRxBw
010 (default)
DccFreq
4
4
3
3
3
2
2
2
1
1
1
0
0
0
000
001
100
101
011
110
111
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100.0
125.0
166.7
200.0
250.0
333.3
400.0
500.0
25.0
31.3
41.7
50.0
62.5
83.3
% of RxBw
0.125
fc in
0.25
0.5
16
8
4
2
1
100.0
125.0
166.7
200.0
250.0
12.5
15.6
20.8
25.0
31.3
41.7
50.0
62.5
83.3
SX1231H
DATASHEET
www.semtech.com