RF65 datasheet(27/72 Pages) ETC2

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Page 27

RF65

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ADVANCED COMMUNICATIONS & SENSING

DATASHEET

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:

FEI = FSTEP × FeiValue

RF65 in Rx mode Preamble-

modulated input signal Signal

level > Sensitivity

Set FeiStart

= 1

FeiDone

= 1

Yes

Read

FeiValue

Figure 11. FEI Process

3.4.16. 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,

FRF. The AFC can be launched:



Each time the receiver is enabled, if AfcAutoOn = 1



Upon user request, by setting bit AfcStart in RegAfcFei, if AfcAutoOn = 0

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