SX1231-31SKB868-EVAL Semtech, SX1231-31SKB868-EVAL Datasheet - Page 32

• Manufacturer Part Number: SX1231-31SKB868-EVAL
• Description: development tool usb kit for sx1231 transceiver...
• Manufacturer: Semtech

signed result is loaded in FeiValue in RegFei, in 2’s complement format. The time required for an FEI evaluation is 4 times
the bit period.
To ensure a proper behavior of the FEI:
The 20 dB bandwidth of the signal can be evaluated as follows (double-side bandwidth):
The frequency error, in Hz, can be calculated with the following formula:
3.5.15. Automatic Frequency Correction
The AFC is based on the FEI block, and therefore the same input signal and receiver setting conditions apply. When the
AFC procedure is done, AfcValue is directly subtracted to the register that defines the frequency of operation of the chip,
F
Rev 4 - Nov 2010
ADVANCED COMMUNICATIONS & SENSING
RF
The operation must be done during the reception of preamble
The sum of the frequency offset and the 20 dB signal bandwidth must be lower than the base band filter bandwidth
Each time the receiver is enabled, if AfcAutoOn = 1
Upon user request, by setting bit AfcStart in RegAfcFei, if AfcAutoOn = 0
. The AFC can be launched:
Preamble-modulated input signal
Figure 12. FEI Process
BW
Signal level > Sensitivity
FEI
SX1231 in Rx mode
20 dB
Set FeiStart
Yes
=
FeiValue
FeiDone
F
=
Read
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= 1
= 1
STEP
2
×
⎛
⎝
×
F
FeiValue
DEV
No
+
BR
------ -
2
⎞
⎠
DATASHEET
www.semtech.com
SX1231