RF69 datasheet(29/81 Pages) ETC2

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RF69

Page 29

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0.5  

3.4.11. FSK Demodulator

The FSK demodulator of the RF69 is designed to demodulate FSK, GFSK, MSK and GMSK modulated signals. It is

most efficient when the modulation index of the signal is greater than 0.5 and below 10:

The output of the FSK demodulator can be fed to the Bit Synchronizer (described in section 3.4.13), to provide the

companion processor with a synchronous data stream in Continuous mode.

3.4.12. OOK Demodulator

The OOK demodulator performs a comparison of the RSSI output and a threshold value. Three different threshold modes

are available, configured through bits OokThreshType in RegOokPeak.

The recommended mode of operation is the "Peak" threshold mode, illustrated in Figure 11:

RSSI

[dBm]

„ ‟ Peak -6dB‟‟ Threshold

„‟ Floor‟‟ threshold defined by

OokFixedThresh

Noise floor of

receiver

Time

Zoom

Decay in dB as defined in

OokPeakThreshStep

Fixed 6dB difference

Period as defined in

OokPeakThreshDec

Figure 11. OOK Peak Demodulator Description

In peak threshold mode the comparison threshold level is the peak value of the RSSI, reduced by 6dB. In the absence of

an input signal, or during the reception of a logical "0", the acquired peak value is decremented by one

OokPeakThreshStep every OokPeakThreshDec period.

When the RSSI output is null for a long time (for instance after a long string of "0" received, or if no transmitter is present),

the peak threshold level will continue falling until it reaches the "Floor Threshold", programmed in OokFixedThresh.

The default settings of the OOK demodulator lead to the performance stated in the electrical specification. However, in

applications in which sudden signal drops are awaited during a reception, the three parameters should be optimized

accordingly.

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