MRF39RA Datasheet, PDF (12/72 Pages) Microchip Technology – Low-Power, Integrated UHF Receiver

MRF39RA
2.4.6 DC CANCELLATION
DC cancellation is required in zero-IF architecture
transceivers to remove any DC offset generated
through self-reception. It is built in the MRF39RA and
its adjustable cutoff frequency (fc) is controlled in
RegRxBw. Table 2-4 shows the available DCC cutoff
frequencies.
TABLE 2-4:
AVAILABLE DCC CUTOFF
FREQUENCIES
DccFreq in RegRxBw
fc in % of RxBw
000
16
001
8
010 (default)
4
011
2
100
1
101
0.5
110
0.25
111
0.125
The default value of DccFreq cutoff frequency is
typically 4% of the RxBw (channel filter BW). The
cutoff frequency of the DCC can however be
increased to slightly improve the sensitivity, under
wider modulation conditions. It is advised to adjust the
DCC setting while monitoring the receiver sensitivity.
2.4.7 COMPLEX FILTER – OOK
In OOK mode the MRF39RA is modified to a low-IF
architecture. The IF frequency is automatically set to
half the single-side bandwidth of the channel filter
(FIF = 0.5 x RxBw). The Local Oscillator is
automatically offset by the IF in the OOK receiver. A
complex filter is implemented on the chip to attenuate
the resulting image frequency by typically 30 dB.
Note:
This filter is automatically bypassed when
receiving FSK signals (ModulationType = 00
in RegDataModul).
DS40001778B-page 12
 2015 Microchip Technology Inc.