LLCC68 datasheet(38/106 Pages) SEMTECH

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LLCC68

Data Sheet

Rev. 1.0

DS.LLCC68.W.APP

July 2019

38 of 106

Semtech

www.semtech.com

6.2 FSK Modem

6.2.1 Modulation Parameter

The FSK modem is able to perform transmission and reception of 2-FSK modulated packets over a range of data rates

ranging from 0.6 kbps to 300 kbps. All parameters are set by using the command SetModulationParams(...). This function

should be called only after defining the protocol.

The bitrate setting is referenced to the crystal oscillator and provides a precise means of setting the bit rate (or equivalently

chip) rate of the radio. In the command SetModulationParams(...), the bitrate is expressed as 32 times the XTAL frequency

divided the real bit rate used by the device. The generic formula is:

FSK modulation is performed inside the PLL bandwidth, by changing the fractional divider ratio in the feedback loop of the

PLL. The high resolution of the sigma-delta modulator, allows for very narrow frequency deviation. The frequency deviation

Fdev is one of the parameters of the function SetModulationParams(...) and is expressed as:

where:

Additionally, in transmission mode, several shaping filters can be applied to the signal. In reception mode, the user needs

to select the best reception bandwidth depending on its conditions. To ensure correct demodulation, the following limit

must be respected for the selection of the bandwidth:

The bandwidth is defined by parameter BW as described in the following table.

Table 6-4: Bandwidth Definition in FSK Packet Type

Value

Bandwidth [kHz DSB]

BW4

0x1F

4.8

BW5

0x17

5.8

BW7

0x0F

7.3

BW9

0x1E

9.7

BW11

0x16

11.7

BW14

0x0E

14.6

BW19

0x1D

19.5

BW23

0x15

23.4

BW29

0x0D

29.3

FXOSC

BitRate

--------------------*32

Fdev

FdevHz

FreqStep

------------------------

FreqStep

XtalFreq

225

------------------------

2*Fdev

 BW

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