MRF89XAM8A-I Datasheet, PDF (63/140 Pages) Microchip Technology – Ultra Low-Power, Integrated ISM Band Sub-GHz Transceiver

MRF89XA
The POLCFV<3:0> bits (PFCREG<7:4>) set f_o, the
center frequency of the polyphase filter when activated.
f_o should always be chosen to be equal to the low
Intermediate Frequency of the receiver (IF2). Because
low IF frequency of the OOK receiver denoted by IF2
can always be replaced by f_o for any calculations or
monitoring purposes.
The following setting is recommended:
f_o = 100 kHz
POLCFV<3:0> = 0011.
The value stored as BUTFILV<3:0> bits
(FILCREG<3:0>) determines f_c, the filter cut-off
frequency. Therefore, f_c should be set according to
Equation 3-12.
EQUATION 3-12:
Again, f_c as a function of the BUTFILV<3:0> bits, is
described in Section 3.4.6, Channel Filters Setting in
OOK Mode.
3.4.5
CHANNEL FILTERS SETTING IN
FSK MODE
f_c, the 3dB cut-off frequency of the Butterworth filter
used in FSK reception, is programmed through the
BUTFILV<3:0> bits (FILCREG<3:0>). However, the
entire receiver chain influences this cut-off frequency.
The channel select and resultant filter bandwidths are
illustrated in Figure 3-7.
Table 4-2 suggests filter settings in FSK mode along
with the corresponding passive filter bandwidth and the
accepted tolerance on the crystal reference.
2^∗(f_c – f_o) > BW_99%,ook + LO_drifts
Where,
f_c is the cut-off frequency
f_o is the center frequency
FIGURE 3-7:
450
400
350
300
250
200
150
100
50
0
0
ACTUAL BW OF BUTTERWORTH FILTER
Butterworth Filter BW, FSK
2
4
6
8
10
Val BUTFILV<3:0> [d]
Actual
BW
Theoretical
BW
12
14
16
© 2010–2011 Microchip Technology Inc.
Preliminary
DS70622C-page 63