C2510Fx / CC2511Fx
0.0
-10.0
-20.0
-30.0
RSSI readout [dBm]
-40.0
-50.0
-60.0
-70.0
-80.0
-90.0
-100.0
-110.0
-120.0
-120 -110 -100 -90
-80
-70
-60
-50
-40
-30
-20
-10
0
Input power [dBm]
250 kBaud, reduced current
500 kBaud
2.4 kBaud
10 kBaud
250 kBaud
Figure 51: Typical RSSI Value vs. Input Power Level for Some Typical Data Rates
14.10.4
Carrier Sense (CS)
14.10.5
CS Absolute Threshold
The Carrier Sense (CS) flag is used as a sync
word qualifier and for CCA. The CS flag can
be set based on two conditions, which can be
individually adjusted:
The absolute threshold related to the RSSI
value depends on the following register fields:
•
•
•
•
AGCCTRL2.MAX_LNA_GAIN
• CS is asserted when the RSSI is above
a programmable absolute threshold, and
de-asserted when RSSI is below the
same threshold (with hysteresis).
AGCCTRL2.MAX_DVGA_GAIN
AGCCTRL1.CARRIER_SENSE_ABS_THR
AGCCTRL2.MAGN_TARGET
• CS is asserted when the RSSI has
increased with a programmable number
of dB from one RSSI sample to the next,
and de-asserted when RSSI has
decreased with the same number of dB.
This setting is not dependent on the
absolute signal level and is thus useful
to detect signals in environments with a
time varying noise floor.
For a given AGCCTRL2.MAX_LNA_GAIN and
AGCCTRL2.MAX_DVGA_GAIN setting the
absolute threshold can be adjusted ±7 dB in
steps of dB using
CARRIER_SENSE_ABS_THR.
1
The MAGN_TARGET setting is a compromise
between blocker tolerance/selectivity and
sensitivity. The value sets the desired signal
level in the channel into the demodulator.
Increasing this value reduces the headroom
for blockers, and therefore close-in selectivity.
It is strongly recommended to use SmartRF®
Carrier Sense can be used as a sync word
qualifier that requires the signal level to be
higher than the threshold for a sync word
search to be performed. The signal can also
be observed on P1_5, P1_6, or P1_7 by
setting IOCFGx.GDOx_CFG=1110 and in the
status register bit PKTSTATUS.CS.
Studio
[8]
to
generate
the
correct
MAGN_TARGET setting.
Table 69 and Table 70 show the typical RSSI
readout values at the CS threshold at 2.4
kBaud and 250 kBaud data rate respectively.
The default CARRIER_SENSE_ABS_THR=0 (0
dB) and MAGN_TARGET=11(33 dB) have been
used.
Other uses of Carrier Sense include the TX-if-
CCA function (see Section 14.10.7 on Page
201) and the optional fast RX termination (see
Section 14.12.3 on Page 206).
CS can be used to avoid interference from e.g.
WLAN.
SWRS055D
Page 200 of 243
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