CC2400 Datasheet, PDF (44/84 Pages) Texas Instruments – 2.4 GHz Low-Power RF Transceiver

CC2400
34 RSSI
CC2400 has a built-in RSSI (Received
Signal Strength Indicator) giving a digital
value that can be read form the
RSSI.RSSI_VAL[7:0] register.
The RSSI reading provides a measure of
the signal power entering the RF input.
The scale is logarithmic, so that
RSSI_VAL provides a value in dB.
The number of samples that are used to
calculate the average signal amplitude is
controlled
by
the
RSSI.RSSI_FILT[1:0] register. The
RSSI filter length (averaging) can be done
over up to 8 symbols. This will determine
the response time of the RSSI.
The RSSI measurement can be referred to
the power at the RF input pins by using
the following equation:
P = RSSI_VAL + RSSI_OFFSET [dBm]
where the nominal value of
RSSI_OFFSET is –54dB. (If the gain in
the LNA/Mixer is changed from the default
settings, the offset is changed.)
A typical plot of the RSSI_VAL reading as
function of input power is shown in Figure
22 (for 1Mbps).
Note that the RSSI function does not take
AGC settings into consideration if the AGC
settings are overridden.
50
40
30
20
10
0
-10
-20
-30
-40
-50
-60
-120 -116 -112 -108 -104 -100 ^{-96 -92 -88 -84 -80 -76 -72 -68 -64 -60 -56 -52 -48 -44 -40 -36 -32 -28 -24 -20 -16 -12 -8 -4 0}
Input level (dBm)
Figure 22. Typical RSSI value vs. input power
1M
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