S2-LPS datasheet(23/73 Pages) STMICROELECTRONICS

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Table 34. Constellation mapping 2-(G)FSK

Format

Symbol

CONST_MAP coding

2-(G)FSK

-FDEV

+FDEV

-FDEV

Table 35. Constellation mapping 4-(G)FSK

Format

Symbol

CONST_MAP coding

4-(G)FSK

-FDEV/3

-FDEV

+FDEV/3

+FDEV

-FDEV

-FDEV/3

+FDEV

+FDEV/3

+FDEV

-FDEV/3

-FDEV

+FDEV

+FDEV/3

-FDEV

-FDEV/3

Furthermore, in the 4-(G)FSK it is also possible to swap the symbols using the 4FSK_SYM_SWAP field (register

PCKTCTRL3) as follows:

(10)

When 4FSK_SYM_SWAP = 0: S0 = <b7b6>

S1 = <b5b4>

S2 = <b3b2>

S3 = <b1b0>

When 4FSK_SYM_SWAP = 1 S0 = <b6b7>

S1 = <b4b5>

S2 = <b2b3>

S3 = <b0b1>

4.4.1.1

Gaussian shaping

In 2-GFSK or 4-GFSK mode, the Gaussian filter BT product can be set by using the register BT_SEL to 1 or 0.5.

The Gaussian filtering is implemented by poly-phase filtering with eight taps per symbol time. In order to further

smooth the filter shape and improve spectral shaping, the output of the filter can be linearly interpolated by setting

the register MOD_INTERP_EN.

A mathematical interpolation factor is applied at each sample of the Gaussian filter output. This factor is 64

for data rates corresponding to DATA_RATE_E < 5, it is automatically scaled as

2DATA_RATE_E−5for5≤

DATA_RATE_E < 11 and it is automatically disabled for DATA_RATE_E = 11.

Note:

The actual interpolation factor achieved may be limited by the minimal frequency resolution of the frequency

synthesizer.

4.4.1.2

ISI cancellation 4-(G)FSK

Since the 4-(G)FSK modulation format strongly suffers from the effect of inter symbol interference, an ISI

cancellation equalizer has been introduced in the demodulator. An equalizer can be enabled, by using the

EQU_CTRL register, with two modes: single pass equalization and dual pass equalization. The best performance

is normally achieved using the dual pass equalizer.

4.4.2

Amplitude modulation

Amplitude modulation OOK and ASK are both supported by the S2-LPS. The ASK selection depends on power

ramping enable.

When OOK is selected, a bit '1' is transmitted with a programmed power, set by register

PA_POWER[PA_LEVEL_MAX_INDEX], and a bit '0' is transmitted without output power (PA off) and specified

by the register PA_POWER[0].

S2-LPS

Digital modulator

DS13831 - Rev 1

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