SX1211 Ver la hoja de datos (PDF) - Semtech Corporation
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SX1211 Datasheet PDF : 92 Pages
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SX1211
ADVANCED COMMUNICATIONS & SENSING
3.3.6. Interpolation Filter
After digital to analog conversion, both I and Q signals are smoothed by interpolation filters. This block low-pass
filters the digitally generated signal, and prevents the alias signals from entering the modulators. Its bandwidth can
be programmed with the register RXParam_InterpFiltTx, and should be set to:
BW
≅
3*
Fdev
+
BR
2
Where Fdev is the programmed frequency deviation as set in MCParam_Freq_dev, and BR is the physical Bit Rate
of transmission.
Notes:
Low interpolation filter bandwidth will attenuate the baseband I/Q signals thus reducing the power of the FSK
signal. Conversely, excessive bandwidth will degrade spectral purity.
For the wideband FSK modulation, for example when operating in DTS mode, the recommended filter setting
can not be reached. However, the impact upon spectral purity will be negligible, due to the already wideband
channel.
3.3.7. Power Amplifier
The Power Amplifier (PA) integrated in the SX1211 operates under a regulated voltage supply of 1.8 V. The
external PA choke inductor is biased by an internal regulator output made available on pin 29 (VR_PA). Thanks to
these features, the PA output power is consistent over the power supply range. This is important for mobile
applications where this allows both predictable RF performance and battery life.
3.3.7.1. Rise and Fall Times Control
In OOK mode, the PA ramp times can be accurately controlled through the MCParam_PA_ramp register. Those
bits directly control the slew rate of VR_PA output (pin 29).
Table 11: PA Rise/Fall Times
MCParam_PA_ramp
00
01
10
11
tVR_PA
3 us
8.5 us
15 us
23 us
tPA_OUT (rise / fall)
2.5 / 2 us
5 / 3 us
10 / 6 us
20 / 10 us
Rev 7 – Sept 2nd, 2008
Page 20 of 92
www.semtech.com
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