S2-LPS datasheet(25/73 Pages) STMICROELECTRONICS

25 / 73 page

Where

fdev_programmedisthefrequencydeviationprogrammedinthechipbytheregistersMOD[1:0](see

Section 4.4.1 Frequency modulation),

fdev_fifo_sampleisthefirstbyteofthebytescouplesampledfromthe

TX_FIFO.

The

fdev_fifo_sampleisinterpretedasa2-complement8-bitnumber,thusitcanbeeitherapositiveora

negative value.

The instantaneous frequency is given by the formula:

Instantaneous frequency in polar mode

f=fc_programmed+ fdev

(12)

The second byte of the TX_FIFO couple drives the PA giving an instantaneous output power.

The output power will be generated according to this value following the same code as the PA_POWER registers

(see Section 4.4.6.1 PA configuration).

Figure 9. Direct polar mode shows how the byte couples are sampled from the TX FIFO and sent to the SYNTH

and PA blocks.

Figure 9. Direct polar mode

As for the normal TX operations, the TX_FIFO samples are consumed and a management of the

TX_FIFO_THRESHOLD is needed to perform transmissions longer than 128 samples.

The transmission is never automatically stopped and a specific command SABORT should be given to terminate

it.

4.4.4

Test modes

4.4.4.1

Continuous wave

The device can be programmed to generate a continuous wave carrier without any modulation. In this way, the

carrier will be continuously transmitted until a SABORT command is sent to the device.

To set the continuous wave the MOD_TYPE field (of the MOD2 register) must be set to 0x77.

4.4.4.2

PN9

It is possible to set a pseudo random binary sequence 9 (PN9) as data source for the modulator. In this way,

these data are continuously modulated until a SABORT command is sent to the device.

The TXSOURCE field (of the PCKTCTRL1 register) must be set to 0x03.

4.4.4.3

Data rate

The data rate programmable is from 0.1 kbps to 500 kbps (see Table 12. General characteristics) for further

details).

The data rate formula that relates the value of the DATARATE_M and DATARATE_E registers to the data rate in

symbol per second is the following:

Data rate formula

S2-LPS

Digital modulator

DS13831 - Rev 1

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