Data Sheet

Page 44
RFM95/96/97/98(W)
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WIRELESS & SENSING PRELIMINARY DATASHEET
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 13. 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.
Optimizing the Floor Threshold
OokFixedThresh determines the sensitivity of the OOK receiver, as it sets the comparison threshold for weak input signals
(i.e. those close to the noise floor). Significant sensitivity improvements can be generated if configured correctly.
Note that the noise floor of the receiver at the demodulator input depends on:
 The noise figure of the receiver.
 The gain of the receive chain from antenna to base band.
 The matching - including SAW filter if any.
 The bandwidth of the channel filters.