LLCC68 datasheet(39/111 Pages) SEMTECH

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LLCC68

Data Sheet

Rev. 1.1

DS.LLCC68.W.APP

Dec 2024

39 of 111

Semtech

LLCC68

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 from 0.6kbps to

500kbps. 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 6-5: Bandwidth Definition in FSK Packet Type (Sheet 1 of 2)

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

BW39

0x1C

39.0

FXOSC

BitRate

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

Fdev

FdevHz

FreqStep

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

FreqStep

XtalFreq

225

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

2*Fdev BR

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