XE1202AI027TRLF Semtech, XE1202AI027TRLF Datasheet - Page 11

• Manufacturer Part Number: XE1202AI027TRLF
• Description: Narrow Band 433/868/915MHz RF Transceiver
• Manufacturer: Semtech

The modulation index, b, of the modulated carrier should meet the following condition:
where ∆f is the frequency deviation and BR is the bit rate.
The bandwidth of the baseband filter (BBW) must be greater than the sum of the frequency offset and the received
signal bandwith, as defined below:
BBW > f
where BBW is the baseband filter bandwidth defined by the RTParam_BW parameter (see the Configuration
Registers section below), f
BW
The FEI function has two modes of operation, defined by the value set in the register “RTParam_Fsel” (see the
Configuration register section below).
4.1.4.1
With the “RTParam_FEI” bit set to “1” and the “RTParam_Fsel” bit set to “1”, the FEI uses frequency correlation to
provide a 2-bit status word, which is stored in the register “DataOut_FEI”. The contents of this register are defined
below in Table 7. The status of this register is provided in the following table, where f
frequency, and f
The value f
an example, for a bit rate of 4.8kbits/s and with FERR = 0.5, f
The FEI-Correlator function works properly only if the input signal is the preamble sequence defined under the
Receiver section above, and if the frequency error to be detected is lower than 20 kHz.
The time diagram of an FEI measurement is similar to that of an RSSI measurement, and is illustrated in Figure 4
below. When the FEI is enabled, the frequency error is periodically measured and the result is stored in the register
“DataOut_FEI” at each rising edge of DATAIN. TS_FE is the wake-up time required after the function has been
enabled to obtain a valid result. For a proper operation, the pulse length on DATAIN has to be higher than 8µs.
© Semtech 2006
SIGNAL
OFFSET
β
is equal to
“RTParam_Fsel” = 1
=
ERR
2
BR
+ BW
∆ ⋅
= FERR * BR, where BR is the bit rate and FERR is a ratio given in the electrical specifications. As
RF
f
is the carrier frequency of the received signal.
≥
⎛
⎜
⎝
SIGNAL
, 2
BR
2
+ f
∆
OFFSET
⎞
⎟
⎠
.
DataOut_FEI
is the difference between the carrier frequency and the LO frequency, and
0 0
0 1
1 0
1 1
Table 7: FEI status description
⏐f
-
(f
(f
LO
LO
LO
12
-f
-f
-f
RF
RF
RF
) > f
) < -f
⏐ ≤ f
ERR
ERR
ERR
ERR
Meaning
is 2.4 kHz.
XE1202A TrueRF™
LO
is the internal local oscillator
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