S2-LPS datasheet(31/73 Pages) STMICROELECTRONICS

31 / 73 page

4.4.5.9

CS blanking

The CS blanking feature prevents data to be received if the RSSI level on the air is below the RSSI threshold (set

by the RSSI_TH field). The feature can be enabled through the CS_BLANKING bit in the ANT_SELECT_CONF

4.4.5.10

Antenna switching

The device implements a switching based antenna diversity algorithm. The antenna switching function allows

controlling an external switch in order to select the antenna providing the highest measured RSSI. The switching

decision is based on a comparison between the received power level on antenna 1 and antenna 2 during the

preamble reception controlling through GPIO an external RF switch in order to select the antenna providing the

highest measured RSSI.

When antenna switching is enabled, the two antennas are repeatedly switched during the reception of the

preamble of each packet, until the carrier sense threshold is reached (static CS mode must be used). From this

point on, the antenna with highest power is selected and switching is frozen. The switch control signal is available

on GPIO and in the MC_STATE[1] register.

The algorithm is controlled by the following parameters:

•

AS_MEAS_TIME: this register/parameter controls the time interval for RSSI measurement. The actual

measurement time is done with the following formula.

Antenna switching measurement time

Tmeas=24∙2CHFLT_E∙2AS_MEAS_TIME

fdig

(15)

In case of FSK modulation, the whole

Tmeasisusedtoletthesignallevelsettleaftertheantennaswitchandone

single measurement is taken at the end of such period.

In case of OOK modulation, after one first interval equal to

Tmeasagainusedtoletthesignallevelsettleafter

the antenna switch, one second interval still equal to

Tmeas,isusedtoperformapeakpowermeasurementand

select the best antenna.

•

AS_ENABLE: this parameter enables the antenna switching function.

4.4.6

Transmitter

The S2-LPS contains an integrated PA capable of transmitting at output levels programmable between -30 dBm to

+14 dBm (+16 dBm in boost mode), at step of 0.5 dB.

The PA is single-ended and has a dedicated pin (TXOUT). The PA output is ramped up and down to prevent

unwanted spectral splatter. In TX mode the PA drives the signal generated by the frequency synthesizer out to the

antenna terminal. Delivered power, as well as harmonic content, depends on the external impedance seen by the

PA. It is possible to program TX to send an unmodulated carrier.

The output stage is supplied from the SMPS through an external choke and is loaded with a LC-type network

which has the function of transforming the impedance of the antenna and filter out the harmonics. The TX and RX

pins are tied directly to share the antenna. During TX, the LNA inputs are internally shorted to ground to allow for

the external network resonance, so minimizing the power loss due to the RX.

4.4.6.1

PA configuration

The PA output power level is programmable in 0.5 dB steps. The user can store up to eight output levels to

provide flexible PA power ramp-up and ramp-down at the start and end of a frequency modulation transmission as

well as ASK modulation shaping.

With the digital power-ramping enabled (PA_RAMP_EN = 1 in the PA_POWER0 register) the ramp starts from the

minimum output power programmed and stops at the programmed maximum value, thus a maximum of 8 steps

can be set up as shown in Figure 10. Output power ramping configuration. The interpolation factor ranges from 64

down to 1 depending on the actual data rate. The assumption is that output power monotonically decrease. Each

step is held for a programmable time interval expressed in terms of bit period units (Tb/8), maximum value is 3

(which means 4×Tb/8=Tb/2). Therefore, the PA ramp may last up to 4 Tb (about 3.3 ms if the bit rate is 1.2 kbit/s).

Tramp= PA_RAMP_STEP_LEN+1 × PA_LEVEL_MAX_IDX+1

8×DataRate

(16)

where DataRate is the transmission data rate expressed in symbols/s.

S2-LPS

Digital modulator

DS13831 - Rev 1

page 31/73

S2-LPS Datasheet(PDF) 31 Page - STMicroelectronics

S2-LPS Datasheet(HTML) 31 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73

Datasheet Download

Link URL