15

AT86RF211

1942C–WIRE–06/02

RSSI Output

The RSSI value can be read as a 6 bits word in the STATUS register. Its value is linear

in dB as plotted below:

Figure 18. Typical RSSI output (board implementation, T = 25°C, V

Note:

Should the RSSI be required for accurate measurement purpose (precision better than 5 dB), then it is possible to measure one

value with a calibrated RF source and store it into the microcontroller, during the production testing.

The RSSI dynamic range is 50 dB from -95 dBm to -45 dBm RF input signal power, over

temperature and power supply ranges. The RSSI LSB’s value weighs about 1.3 dB in

the linear area. The RSSI value is measured from the IF2 chain.

The RSSI is periodically measured thanks to a successive approximation ADC with a

12 µs clock. Thereafter, the time needed to complete the right code depends on the

power step: a 10 dB step on the aerial leads to a 10/1.3 = 8 clock cycles, i.e. 96 µs (full

range from code 0 to 63 = 756 µs). Its value can be compared with a user predefined

value (TRSSI), so that the demodulated data is enabled only if the RSSI value is above

this threshold. Some hysteresis effect may be added (see CTRL1 register’s content).

The AT86RF211 also has the possibility to measure another voltage. The ADC measur-

ing the RSSI can be turned into voltage or discriminator output DC level measurement.

RSSI Output

0

10

20

30

40

50

60

70

-110

-100

-90

-80

-70

-60

-50

-40

-30

Power Level at Antenna Input Port (dBm)

Dynam ic Range: 50dB

Dispersion: +/-5dB