SM1212E433 Semtech, SM1212E433 Datasheet - Page 25

• Manufacturer Part Number: SM1212E433
• Description: RF Module For SX1212
• Manufacturer: Semtech
• Series: -r
• Type: Transceiver, ISMr

Specifications of SM1212E433

• Frequency: 433MHz
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• For Use With/related Products: SX1212E

As can be seen from Figure 17, the required bandwidth of this filter varies between the two demodulation modes.
The bits RXParam_ButterFilt set fc, the cutoff frequency of the filter. As we are in a Zero-IF configuration, the FSK
lobes are centered around the virtual “DC” frequency. The choice of fc should be such that the modulated signal
falls in the filter bandwidth, anticipating the Local Oscillator frequency drift over the operating temperature and
aging of the device:
Please refer to the charts in section 3.4.5 for an accurate overview of the filter bandwidth vs. setting.
The bits RXParam_PolypFilt_center set fo, the center frequency of the polyphase filter when activated. fo should
always be chosen to be equal to the low Intermediate Frequency of the receiver (IF2). This is why, in the GUI
described in section 7.2.1 of this document, the low IF frequency of the OOK receiver denoted IF2 has been
replaced by fo.
The following setting is recommended:
The value stored in RXParam_ButterFilt determines fc, the filter cut-off frequency. So the user should set fc
according to:
Again, fc as a function of RXParam_ButterFilt is given in the section 3.4.6.
Fc, the 3dB cutoff frequency of the Butterworth filter used in FSK reception, is programmed through the bit
RXParam_ButterFilt. However, the whole receiver chain influences this cutoff frequency. Thus the channel select
and resultant filter bandwidths are summarized in the following chart:
Rev 2 – June 18th, 2009
ADVANCED COMMUNICATIONS & SENSING
FSK mode: The 99% energy bandwidth of an FSK modulated signal is approximated to be:
OOK mode: The 99% energy bandwidth of an OOK modulated signal is approximated to be:
3.4.5. Channel Filters Setting in FSK Mode
2
BW
2
RXParam
fo
( *
*
BW
=
99
fc
fc
100
%,
99
−
>
FSK
%,
fo
kHz
OOK
BW
)
Page 25 of 77
_
=
>
PolypFilt
2
99
BW
=
*
%,
Tbit
⎡
⎢ ⎣
99
FSK
2
Fdev
%,
OOK
+
=
=
+
LO
. 2
+
"
LO
0011
BR
BR
2
drifts
drifts
⎤
⎥ ⎦
"
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SX1212