SM1211E915TOPIC Semtech, SM1211E915TOPIC Datasheet - Page 20

• Manufacturer Part Number: SM1211E915TOPIC
• Description: KIT PICTAIL EXT FOR SX1211
• Manufacturer: Semtech
• Type: Transceiver, UHFr

Specifications of SM1211E915TOPIC

• Frequency: 915MHz
• For Use With/related Products: SX1211
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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:
Where Fdev is the programmed frequency deviation as set in MCParam_Freq_dev, and BR is the physical Bit Rate
of transmission.
Notes:
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.
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
Rev 7 – Sept 2
ADVANCED COMMUNICATIONS & SENSING
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.
00
01
10
11
3.3.6. Interpolation Filter
3.3.7. Power Amplifier
nd
, 2008
3.3.7.1. Rise and Fall Times Control
t
3 us
8.5 us
15 us
23 us
VR_PA
t
2.5 / 2 us
5 / 3 us
10 / 6 us
20 / 10 us
PA_OUT
(rise / fall)
BW
3
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

Fdev
BR
2
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