NXP Semiconductors MKW01Z128, Reference Manual, Page: 76 / 884

Sub 1 GHz Transceiver Architecture Description
MKW01xxRM Reference Manual, Rev. 3, 04/2016
Freescale Semiconductor, Inc. 5-21
5.7.13 Frequency Error Indicator (FEI)
This function provides information about the frequency error of the local oscillator (LO) compared with
the carrier frequency of a modulated signal at the input of the receiver. When the FEI block is launched,
the frequency error is measured and the 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 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
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:
Figure 5-10. FEI Process
BW
20dB
2 F
DEV
BR
2
-------- +
 
 

=
FEI F
STEP
FeiValue

=
SX1231 in Rx mode
Preamble-modulated input signal
Signal level > Sensitivity
Set FeiStart
= 1
FeiDone
= 1
No
Yes
Read
FeiValue
MKW01