CC1110Fx / CC1111Fx
• 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.
MAX_DVGA_GAIN[1:0]
00
01
10
11
000
001
010
011
100
101
110
111
-99
-93
-87
-85
-82
-80
-78
-76
-73
-70
-81.5
-78.5
-76
-97
-90.5
-87
-93.5
-91.5
-90.5
-88
-86
-74
-84
-72.5
-70
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.
-82.5
-78.5
-76
-84.5
-82.5
-67
-64
Table 70: Typical RSSI Value in dBm at CS
Threshold with Default MAGN_TARGETat 2.4
kBaud
Other uses of Carrier Sense include the TX-if-
CCA function (see Section 14.10.7 on page
198) and the optional fast RX termination (see
Section 14.12.3 on page 203).
MAX_DVGA_GAIN[1:0]
00
01
10
11
000
001
010
011
100
101
110
111
-96
-90
-84
-78.5
-77.5
-75
CS can be used to avoid interference from
other RF sources in the ISM bands.
-94.5
-92.5
-91
-89
-83
-87
-81
-85
-78.5
-76
-73
14.10.5 CS Absolute Threshold
-87.5
-85
-82
-70
The absolute threshold related to the RSSI
value depends on the following register fields:
-79.5
-76.5
-72
-73.5
-70.5
-66
-67.5
-65
-83
•
•
•
•
AGCCTRL2.MAX_LNA_GAIN
AGCCTRL2.MAX_DVGA_GAIN
AGCCTRL1.CARRIER_SENSE_ABS_THR
AGCCTRL2.MAGN_TARGET
-78
-60
Table 71: Typical RSSI Value in dBm at CS
Threshold with Default MAGN_TARGETat 250
kBaud
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.
If the threshold is set high, i.e. only strong
signals are wanted, the threshold should be
adjusted upwards by first reducing the
1
MAX_LNA_GAIN
value
and
then
the
MAX_DVGA_GAIN value. This will reduce
power consumption in the receiver front end,
since the highest gain settings are avoided.
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®
14.10.6 CS Relative Threshold
The relative threshold detects sudden changes
in the measured signal level. 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. The register
field AGCCTRL1.CARRIER_SENSE_REL_THR
is used to enable/disable relative CS, and to
select threshold of 6 dB, 10 dB or 14 dB RSSI
change
Studio
[9]
to
generate
the
correct
MAGN_TARGET setting. Table 70 and Table 71
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.
For other data rates the user must generate
similar tables to find the CS absolute
threshold.
14.10.7 Clear Channel Assessment (CCA)
The Clear Channel Assessment CCA) is used
to indicate if the current channel is free or
busy. The current CCA state is viewable on
SWRS033E
Page 198 of 239
TAOS [ TEXAS ADVANCED OPTOELECTRONIC SOLUTIONS ]
