RF96 datasheet(47/121 Pages) HOPE

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Page 47

RF96/97/98

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WIRELESS & SENSING

PRELIMINARY

DATASHEET

4.2.3.4. Frequency Error Indicator

This frequency error indicator measures the frequency error between the programmed RF centre frequency and the carrier

frequency of the modulated input signal to the receiver. When the FEI is performed, 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 bit

periods.

To ensure correct operation of the FEI:

 The measurement must be launched 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. i.e.

The whole modulated spectrum must be received.

The 20 dB bandwidth of the signal can be evaluated as follows (double-side bandwidth):

× 



+ -------



20d B

FDEV

2 



The frequency error, in Hz, can be calculated with the following formula:

FEI = F

STEP

× FeiValue

RF96/7/8 in Rx mode Preamble-

modulated input signal Signal

level > Sensitivity

Set FeiStart

= 1

FeiDone

= 1

Yes

Read

FeiValue

Figure 16. FEI Process

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