XE1203F データシートの表示（PDF） - Semtech Corporation
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XE1203F Datasheet PDF : 36 Pages
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XE1203F
4.1.8 Frequency Error Indicator – FEI
When enabled this function provides an indication of the frequency error of the local oscillator compared with the
received carrier frequency. For guaranteed operation of the FEI function the following two conditions should be met:
1) The modulation index, β, should meet the following condition:
β
=
2⋅∆f
BR
≥ 2,
where: ∆f = frequency deviation of the modulated input signal, BR = input data bit-rate.
2) The bandwidth of the baseband filter (BBW) must be greater than the sum of the frequency offset and the
received peak signal bandwidth, as defined below:
BBW > fOFFSET + BWSIGNAL
where BBW is the baseband filter bandwidth defined by the RTParam_BW register. fOFFSET is the difference
between
the
carrier
frequency and the
LO frequency,
and BWSIGNALis equal
to
BR
2
+ ∆f
.
Note on the timing for FEI measurement: The timing diagram of the FEI measurement process is illustrated in
Figure 7 below. As long as the FEI function remains enabled, the frequency error is continuously measured every
2/BR seconds, starting TS_FEI (see Paragraph 3.2.2) after the FEI function is enabled. The measurement results
are loaded into the status registers Dataout_MSB_fei and Dataout_LSB_fei each time the Dataout_LSB_fei register
is read through the 3-wire serial interface. In the diagram below, Saout_fei is generated internally during a read
sequence from the “Dataout_LSB_fei ‘’ status register.
RTParam_FEI
EN
fei_out
TS_FEI
first
evaluation
val0
val1
2/BR
val2
val3
val4 0
saout_fei
Dataout_MSB_fei&
xxx
Dataout_LSB_fei
val1
val3
Figure 7: Timing diagram of the FEI measurement process
The maximum frequency of SCK during the FEI read operation is 100 kHz. When using the Konnex standard, the
bit ADParam_enable_konnex Configuration Register must be set to ‘1’.
© Semtech 2007
www.semtech.com
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