mrf89xa Microchip Technology Inc., mrf89xa Datasheet - Page 70

• Manufacturer Part Number: mrf89xa
• Description: Ultra-low Power, Integrated Ism Band Sub-ghz Transceiver
• Manufacturer: Microchip Technology Inc.

3.4.8
The effect of the f
OOK modes:
3.4.8.1
In FSK mode, the f
FDVAL<7:0> bits (FDEVREG<7:0>), sets sampling fre-
quencies on the receiver. The user should program the
right values to make it consistent with the frequency
deviation of the FSK signal that is received.
3.4.8.2
The frequency deviation f
sets the sampling rate of the RSSI block. It is therefore
necessary to set f
frequency, IF2, of 100 kHz:
3.4.9
The FSK demodulator provides data polarity informa-
tion based on the relative phase of the input I and Q sig-
nals at the baseband. Its outputs can be fed to the Bit
Synchronizer to recover the timing information. The
user can use the raw, unsynchronized, output of the
FSK demodulator in Continuous mode.
The FSK demodulator of the MRF89XA operates effec-
tively for FSK signals with a modulation index greater
than or equal to two, as shown in Equation 3-13.
FIGURE 3-11:
DS70622B-page 70
MRF89XA
f
FDVAL<7:0> = 00000011
dev
RSSI
(dB)
= IF2 = 100 kHz
f
FSK DEMODULATOR
dev
FSK RX Mode
OOK RX Mode
SETTING IN RECEIVE MODE
dev
dev
setting is different for FSK and
OOK DEMODULATOR OVERVIEW
dev
to the recommended low-IF
dev
setting as configured by
, as described previously,
Zoom
OOKTHPV<2:0>
Period as defined in
OOKTHSV<2;0>
Decay in dB as defined in
Preliminary
EQUATION 3-13:
3.4.10
The OOK demodulator performs a comparison of the
RSSI output and a threshold value. Three different
threshold modes are available, which can be pro-
grammed through the OOKTYP<1:0> bits (DMO-
DREG<4:3>).
The recommended mode of operation is the “Peak”
Threshold mode, as illustrated in Figure 3-11.
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 based on the step value of the OOKTHSV<2:0>
bits (OOKCREG<7:5>) for every period value based on
OOKTHPV<2:0> bits (OOKCREG<4:2>).
When the RSSI output is null for a long time (for exam-
ple, after a long string of zeros is received, or if no
transmitter is present), the peak threshold level will
continue falling until it reaches the “Floor Threshold”
that is programmed through the FTOVAL<7:0> bits
(FLTHREG<7:0>).
The default settings of the OOK demodulator lead to
the performance stated in Section 5.0 “Electrical
Characteristics”.
Fixed 6dB difference
OOK DEMODULATOR
β
=
© 2010 Microchip Technology Inc.
------------------ -
BRVAL
2
''Peak -6 dB'' Threshold
''Floor'' threshold defined by
FTOVAL<7:0>
Noise floor of
receiver
•
f
dev
≥
2
Time