SX1211 Просмотр технического описания (PDF) - Semtech Corporation
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SX1211 Datasheet PDF : 92 Pages
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ADVANCED COMMUNICATIONS & SENSING
SX1211
In OOK mode, the phase difference between the I and Q channels is kept constant (independent of the transmitted
data). Thus, the first stage of up-conversion creates a fixed frequency signal at the low IF = Fdev (This explains
why the transmitted OOK spectrum is offset by Fdev).
OOK Modulation is accomplished by switching on and off the PA and PA regulator stages. By convention:
DATA =''1''⇒ PAon
DATA =''0''⇒ PAoff
After the interpolation filters, a set of four mixers combines the I and Q signals and converts them into a pair of
complex signals at the second intermediate frequency, equal to 1/8 of the LO frequency, or 1/9 of the RF
frequency. These two new I and Q signals are then combined and up-converted to the final RF frequency by two
quadrature mixers fed by the LO signal. The signal is pre-amplified, and then the transmitter output is driven by a
final power amplifier stage.
3.3.2. Bit Rate Setting
In Continuous transmit mode, setting the Bit Rate is useful to determine the frequency of DCLK. As explained in
section 5.3.2, DCLK will trigger an interrupt on the uC each time a new bit has to be transmitted.
BR
=
64 *
[1 +
FXTAL
val(MCParam
_
BR)]
3.3.3. Alternative Settings
Bit rate, frequency deviation and TX interpolation filter settings are a function of the reference oscillator crystal
frequency, FXTAL. Settings other than those programmable with a 12.8 MHz crystal can be obtained by selection of
the correct reference oscillator frequency. Please contact your local Semtech representative for further details.
3.3.4. Fdev Setting in FSK Mode
The frequency deviation, Fdev, of the FSK transmitter is programmed through bits MCParam_Freq_dev:
Fdev
=
32
* [1
+
FXTAL
val(MCParam _
Freq
_
dev)]
For correct operation the modulation index ß should be such that:
β = 2 * Fdev ≥ 2
BR
It should be noted that for communications between a pair of SX1211s, that Fdev should be at least 33 kHz to
ensure a correct operation on the receiver side.
3.3.5. Fdev Setting in OOK Mode
Fdev has no physical meaning in OOK transmit mode. However, as has been shown - due to the DDS baseband
signal generation, the OOK signal is always offset by “-Fdev” (see formulas is section 3.2.8). It is suggested that
Fdev retains its default value of 100 kHz in OOK mode.
Rev 7 – Sept 2nd, 2008
Page 19 of 92
www.semtech.com
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