S2-LPS datasheet(22/73 Pages) STMICROELECTRONICS

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Table 31. Resolution frequency

fxo [MHz]

High band resolution [Hz]

Low band resolution [Hz]

12.4

6.2

The fc is the frequency related to the channel specified. RF channels can be defined using the CHSPACE and

CHNUM registers. In this way, it is possible to change faster the channel by changing just an 8-bits register,

allowing the setting of 256 channels and frequency-hopping sequences. The actual channel spacing is from 793

Hz to 202342 Hz in 793 Hz steps for the 26 MHz configuration and from 1587 to 404685 Hz in 1587 Hz steps for

the 52 MHz configuration.

Table 32. Channel spacing resolution

fxo [MHz]

Channel spacing resolution [Hz]

793.45

4.4

Digital modulator

The S2-LPS supports frequency modulation: 2-FSK, 4-FSK, 2-GFSK, 4-GFSK as well amplitude modulation OOK

and ASK. Using register, the user can also program an unmodulated carrier for lab test and measurement.

A special mode, direct polar modulation, allows building specific modulation scheme controlling directly the

amplitude and the frequency of the carrier synthesized. The register MOD_TYPE is used to select one of the

following modulation scheme.

Table 33. Modulation scheme

MOD_TYPE

Modulation scheme

0000b

2-FSK

0001b

4-FSK

0010b

2-GFSK

0011b

4-GFSK

0101b

ASK/OOK

0110b

Direct polar (TX only)

0111b

4.4.1

Frequency modulation

For frequency modulation 2-(G)FSK and 4-(G)FSK the frequency deviation can be tuned in wide range that

depends on

fxo(XTALfrequency)accordingthefollowingformula:

Frequency deviation

fdev=

fXO219·roundD·FDEV_M·B8

D·B if FDEV_E=0

fXO219·roundD·256+FDEV_M·2FDEV_E−1·B8

D·B

if FDEV_E >0

(9)

Where

fxoistheXTALoscillationfrequency,DisthereferencedividerandBisthebandselector.

The frequency deviation programmed corresponds to the deviation of the outer constellation symbols. The

deviation of the inner symbols is 1/3 of such programmed values, as reported in the table below, where 4 options

are available.

Furthermore, since the payload is normally arranged in bytes, the arrangement can change the mapping for both

2-(G)FSK and 4-(G)FSK modulations, by using the CONST_MAP (register MOD1), in the following way:

S2-LPS

Digital modulator

DS13831 - Rev 1

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