SM1211E915TOPIC Semtech, SM1211E915TOPIC Datasheet - Page 24

• Manufacturer Part Number: SM1211E915TOPIC
• Description: KIT PICTAIL EXT FOR SX1211
• Manufacturer: Semtech
• Type: Transceiver, UHFr

Specifications of SM1211E915TOPIC

• Frequency: 915MHz
• For Use With/related Products: SX1211
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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.
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.
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.
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.
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.
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.
Rev 7 – Sept 2
ADVANCED COMMUNICATIONS & SENSING
3.4.2. LNA and First Mixer
3.4.3. IF Gain and Second I/Q Mixer
3.4.4. Channel Filters
nd
, 2008
3.4.4.1. Passive Filter
3.4.4.2. Active Filter
-f
C
Polyphase filter for OOK ( RXParam_PolyFilt_on=’’1’’ )
-f
3
o
Figure 17: Active Channel Filter Description
*
Low-pass filter for FSK ( RXParam_PolyFilt_on=’’0’’)
Fc
-f
C
ButterfFil
t
BW
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0
0
passive
,
filter
the polyphase filter
Canceled side of
4
f
C
*
Fc
ButterFilt
f
f
requency
requency
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