RFM63B Datasheet, PDF (24/90 Pages) List of Unclassifed Manufacturers – ISM TRANSCEIVER MODULE V1.1

RFM63B
ADVANCED COMMUNICATIONS & SENSING
or to fill the FIFO buffers with glitch-free data in Buffered mode. The operation of the receiver is now described in
detail.
Note: Image rejection is achieved by the SAW filter.
3.4.2. LNA and First Mixer
In receive mode, the RFIO pin is connected to a fixed gain, common-gate, Low Noise Amplifier (LNA). The
performance of this amplifier is such that the Noise Figure (NF) of the receiver can be estimated to be ≈7 dB.
3.4.3. IF Gain and Second I/Q Mixer
Following the LNA and first down-conversion, there is an IF amplifier whose gain can be programmed from -
13.5 dB to 0 dB in 4.5 dB steps, via the register MCParam_IF_gain. The default setting corresponds to 0 dB gain,
but lower values can be used to increase the RSSI dynamic range. Refer to section 3.4.7 for additional information.
3.4.4. Channel Filters
The second mixer stages are followed by the channel select filters. The channel select filters have a strong
influence on the noise bandwidth and selectivity of the receiver and hence its sensitivity. Each filter comprises a
passive and active section.
3.4.4.1. Passive Filter
Each channel select filter features a passive second-order RC filter, with a bandwidth programmable through the
bits RXParam_PassiveFilt. As the wider of the two filters, its effect on the sensitivity is negligible, but its bandwidth
has to be setup instead to optimize blocking immunity. The value entered into this register sets the single side
bandwidth of this filter. For optimum performance it should be set to 3 to 4 times the cutoff frequency of the active
Butterworth (or polyphase) filter described in the next section.
3.4.4.2. Active Filter
The ‟fine‟ channel selection is performed by an active, third-order, Butterworth filter, which acts as a low-pass filter
for the zero-IF configuration (FSK), or a complex polyphase filter for the Low-IF (OOK) configuration. The
RXParam_PolypFilt_on bit enables/disables the polyphase filter.
Low-pass filter for FSK ( RXParam_PolyFilt_on=‟‟0‟‟)
-f_C
0
f_C
Polyphase filter for OOK ( RXParam_PolyFilt_on=‟‟1‟‟ )
frequency
Canceled side of
the polyphase filter
-fC
-fo
0
Figure 17: Active Channel Filter Description
frequency
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