MRF39RA Datasheet, PDF (15/72 Pages) Microchip Technology – Low-Power, Integrated UHF Receiver

MRF39RA
2.4.11 FSK DEMODULATOR
The FSK demodulator of the MRF39RA 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, see
Equation 2-7.
EQUATION 2-7: MODULATION INDEX
0.5   = ^2--------_B--^F--_R--^D---^E----^V-  10
2.4.12 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 as illustrated in Figure 2-6.
The output of the FSK demodulator can be fed to the
bit synchronizer as described in Section 2.4.14 “Bit
Synchronizer” to provide the companion processor
with a synchronous data stream in Continuous mode.
FIGURE 2-6:
R SSI
( dBm)
OOK PEAK DEMODULATOR DESCRIPTION
‘’Peak -6 dB’’ Threshold
‘’Floor’’ threshold defined by
OokFixedThresh
Noise floor of
receiver
Zoomm
Decay in dB as defined in
OokPeakT hreshStep
Period as defined in
OokPeakThreshDec
In Peak Threshold mode the comparison threshold level
is the peak value of the RSSI, reduced by 6 dB. 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
continues to fall 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
must be optimized accordingly.
 2015 Microchip Technology Inc.
Fixed 6 dB difference
Tim e
DS40001778B-page 15