RFM95 datasheet(44/121 Pages) HOPERF

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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.

RFM95 Datasheet(PDF) 44 Page - Shenzhen Hope Microelectronics Co., Ltd.