CC1000-RTR2 datasheet(33/59 Pages) TI2

33 / 59 page

CC1000

SWRS048A

Page 33 of 55

22. RSSI output

CC1000 has a built-in RSSI (Received

Signal

Strength

Indicator)

giving

analogue output signal at the RSSI/IF pin.

The IF_RSSI bits in the FRONT_END

function is enabled, the output current of

this pin is inversely proportional to the

input signal level. The output should be

terminated in a resistor to convert the

current output into a voltage. A capacitor

is used in order to low-pass filter the

signal.

The RSSI voltage range from 0 – 1.2 V

when using a 27 k

Ω terminating resistor,

giving approximately 50 dB/V. This RSSI

voltage can be measured by an A/D

converter. Note that a higher voltage

means

lower

input

signal.

The RSSI measures the power referred to

the RF_IN pin. The input power can be

calculated using the following equations:

P = -51.3 VRSSI– 49.2 [dBm] at 433 MHz

P = -50.0 VRSSI– 45.5 [dBm] at 868 MHz

The external network for RSSI operation is

shown in Figure 21. R281 = 27 k

Ω, C281

= 1nF.

A typical plot of RSSI voltage as function

of input power is shown in Figure 22.

Figure 21. RSSI circuit

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.1

1.2

1.3

-105 -100 -95

-90

-85

-80

-75

-70

-65

-60

-55

-50

dBm

433Mhz

868Mhz

Figure 22. RSSI voltage vs. input power

RSSI/IF

TO ADC

CC1000

R281

C281

RSSI/IF

TO ADC

CC1000

R281

C281

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