SX1211I084TRT(2007) Просмотр технического описания (PDF) - Semtech Corporation
Номер в каталоге
Компоненты Описание
производитель
SX1211I084TRT
(Rev.:2007)
(Rev.:2007)
Semtech Corporation
SX1211I084TRT Datasheet PDF : 73 Pages
| |||
ADVANCED COMMUNICATIONS & SENSING
Low-pass filter for FSK ( RXParam_PolyFilt_on=’’0’’)
SX1211
-fC
0
fC
Polyphase filter for OOK ( RXParam_PolyFilt_on=’’1’’ )
frequency
Canceled side of
polyphase filter
-fC
-fo
0
Figure 18: Active Channel Filter Description
frequency
As can be seen from Figure 18, the required bandwidth of this filter varies between the two demodulation modes.
FSK mode: The 99% energy bandwidth of an FSK modulated signal is approximated to be:
BW99%,FSK
=
2
*
Fdev
+
BR
2
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 drift over the operating temperature and lifespan of the
device:
2 * fc > BW99%,FSK + LOdrifts
Please refer to the charts in section 3.4.5 for an accurate overview of the filter bandwidth vs. setting.
OOK mode: 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. This is
why, in the GUI described in section 3.2.9.1 of this document, the low IF frequency of the OOK receiver
denoted IF2 has been replaced by fo. The following setting is recommended:
fo = 100kHz
RXParam _ PolypFilt ="0011"
Then, the 99% energy bandwidth of an OOK modulated signal is approached by:
BW99%,OOK
=
2
Tbit
= 2.BR
The value stored in RXParam_ButterFilt determines fc, the filter cut-off frequency. So the user should set fc
according to:
2 * ( fc − fo) > BW99%,OOK + LOdrifts
V3.0 – august 15th, 2007
Page 26 of 73
www.semtech.com
Share Link: