XE1202A データシートの表示（PDF） - Semtech Corporation

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XE1202A

433 MHz / 868 MHz / 915 MHz Low-Power, Integrated UHF Transceiver

Semtech Corporation 

XE1202A TrueRF™

The modulation index, b, of the modulated carrier should meet the following condition:

β = 2⋅∆f ≥ 2,

BR

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 > fOFFSET + BWSIGNAL

where BBW is the baseband filter bandwidth defined by the RTParam_BW parameter (see the Configuration

Registers section below), fOFFSET is the difference between the carrier frequency and the LO frequency, and

BWSIGNALis

equal

to

⎜⎛ BR

⎝2

+ ∆f

⎟⎞ .

⎠

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 “RTParam_Fsel” = 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 fLO is the internal local oscillator

frequency, and fRF is the carrier frequency of the received signal.

DataOut_FEI

00

01

10

11

Meaning

⏐fLO-fRF⏐ ≤ fERR

-

(fLO-fRF) > fERR

(fLO-fRF) < -fERR

Table 7: FEI status description

The value fERR = FERR * BR, where BR is the bit rate and FERR is a ratio given in the electrical specifications. As

an example, for a bit rate of 4.8kbits/s and with FERR = 0.5, fERR is 2.4 kHz.

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

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