CC2500-RTR1 datasheet(36/99 Pages) TI1

36 / 99 page

CC2500

SWRS040C

Page 36 of 89

IOCFGx.GDOx_CFG

=14 and in the status

Other uses of Carrier Sense include the TX-if-

CCA function (see Section 17.5 on page 37)

and the optional fast RX termination (see

Section 19.7 on page 43).

CS can be used to avoid interference from e.g.

WLAN.

17.4.1 CS Absolute Threshold

The absolute threshold related to the RSSI

value depends on the following register fields:



AGCCTRL2.MAX_LNA_GAIN



AGCCTRL2.MAX_DVGA_GAIN



AGCCTRL1.CARRIER_SENSE_ABS_THR



AGCCTRL2.MAGN_TARGET

For a given AGCCTRL2.MAX_LNA_GAIN and

AGCCTRL2.MAX_DVGA_GAIN

setting

the

absolute threshold can be adjusted ±7 dB in

steps

using

CARRIER_SENSE_ABS_THR

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

Studio

[5]

generate

the

correct

MAGN_TARGET

setting.

Table 26 and Table 27 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=3 (33 dB) have been

used.

For other data rates the user must generate

similar

tables

find

the

absolute

threshold.

MAX_DVGA_GAIN[1:0]

000

-99

-93

-87

-81.5

001

-97

-90.5

-85

-78.5

010

-93.5

-87

-82

-76

011

-91.5

-86

-80

-74

100

-90.5

-84

-78

-72.5

101

-88

-82.5

-76

-70

110

-84.5

-78.5

-73

-67

111

-82.5

-76

-70

-64

Table 26: Typical RSSI Value in dBm at CS

Threshold with Default MAGN_TARGET at 2.4

kBaud

MAX_DVGA_GAIN[1:0]

000

-96

-90

-84

-78.5

001

-94.5

-89

-83

-77.5

010

-92.5

-87

-81

-75

011

-91

-85

-78.5

-73

100

-87.5

-82

-76

-70

101

-85

-79.5

-73.5

-67.5

110

-83

-76.5

-70.5

-65

111

-78

-72

-66

-60

Table 27: Typical RSSI Value in dBm at CS

Threshold with Default MAGN_TARGET at 250

kBaud

If the threshold is set high, i.e. only strong

signals are wanted, the threshold should be

adjusted

upwards

first

reducing

the

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.

17.4.2 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

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