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11

XE1202A TrueRF™

4.1.3

RSSI

When enabled, this function provides an RSSI (Received Signal Strength Indication) based on the signal at the

output of the base-band filter. To enable the RSSI function, the bit “RTParam_RSSI” should be set to “1” (see the

Configuration register section below). When enabled, the status of the RSSI is a 2-bit word stored in register

“DataOut_RSSI”, which can be read via the serial control interface. The contents of the register are defined in

operated in A-mode. The thresholds VTHRi are the thresholds at the output of the base-band filter divided by the

gain between the input of the receiver and this output.

DataOut_RSSI

Description

0 0

0 1

1 0

1 1

Table 6: RSSI status description

Two ranges, each of three VTHRi thresholds are defined and selected via the setting of the register

“RTParam_RSSR”, to provide an overall RSSI range of typically 25 dB.

The timing diagram of an RSSI measurement is illustrated by Figure 3 below. When the RSSI function has been

activated the signal strength is periodically measured and the result is stored in the register “DataOut_RSSI” at

each rising edge of DATAIN. TS_RS is the wake-up time required after the function has been enabled to ensure

that a valid reading of RSSI is obtained. For a proper operation, the pulse length on DATAIN has to be higher than

8µs.

xxx

val1

val2

val3

val4

0

val1

val4

xxx

TS_RS

datain

RSSI_out

(internal signal)

/en

RTParam_RSSI

DtaOut_RSSI

TS_RSM

Figure 3: RSSI measurement timing diagram

For applications where a valid RSSI reading is required within as short a time frame as possible, enabling the RSSI

during receiver mode 010 instead of 100 (see the definition of TS_RS in Table 4) allows a valid RSSI within 1 ms of

valid data being received.

4.1.4

Frequency Error Indicator - FEI

When enabled, this function provides an indication of the frequency error of the local oscillator compared with the

received carrier frequency. For guaranteed operation of the FEI function, the following two conditions should be

satisfied.