SX1235 datasheet(98/104 Pages) SEMTECH

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SX1235

WIRELESS & SENSING

DATASHEET

Rev 1 - December 2012

7.8. ETSI Category 1 Quick Start

To correctly configure the SX1235 for ETSI category 1 operation, it is necessary to enable some specific functionality within

the receiver. The following description highlights the settings required to enable and realize the category 1 performances of

the SX1235.

7.8.1. PLL Settings

The SX1235 features a single PLL for use in reception. Correctly configured, the PLL becomes the component of the

receiver system that has the greatest contribution to the adjacent channel performances of the receiver. By minimizing the

phase noise, the rejection afforded in the adjacent channels is increased.

The default PLL bandwidth setting provides the lowest phase noise in the 12.5 kHz and 25 kHz frequency offsets.

However, by modification of the loop gain setting it is possible to further improve the phase noise in this frequency range.

The RegPllGopt (address 0x5F) should be written to value 0x37. With this setting the resultant phase noise is shown in the

figure below.

Figure 59. SX1235 Optimised Phase Noise at 12.5 kHz and 25 kHz

7.8.2. Channel Filter Settings

The dominance of the phase noise on the adjacent channel rejection performance of the SX1235 assumes that the

receiver channel filtration is correctly configured. Two receiver channel filter bandwidths are accessible during the

reception of data: The first, the AFC bandwidth is the bandwidth used during reception of preamble and alignment of the

receiver. The second, the communication (Rx) bandwidth is that used for the ensuing communication phase. These must

be suitably wide that the total crystal error and modulation bandwidth of the signal can be accommodated by the receiver

during the AFC phase. The narrower communication bandwidth must then be at least as wide as the received signal’s

modulation bandwidth. To ensure the highest link quality the -20 dB bandwidth of the receiver filter is declared.

The figure below illustrates the difference between these three filter settings and the conventions used in the use of either

double or single side band used.

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