CC1020-RTR1 datasheet(33/91 Pages) TI

33 / 91 page

CC1020

SWRS046

Page 33 of 92

Sensitivity [dBm]

Data rate

[kBaud]

Channel spacing

[kHz]

Deviation

[kHz]

Filter BW

[kHz]

NRZ

mode

Manchester

mode

UART

mode

2.4

12.5

± 2.025

12.288

-112

-116

-112

4.8

± 2.475

19.2

-111

-112

-111

9.6

± 4.95

25.6

-109

-110

-109

19.2

100

± 9.9

51.2

-107

38.4

150

± 19.8

102.4

-103

76.8

200

± 36.0

153.6

-99

-100

-99

153.6

500

± 72.0

307.2

-94

Table 20. Typical receiver sensitivity as a function of data rate at 868 MHz, FSK

modulation, BER = 10

−3, pseudo-random data (PN9 sequence)

12.5. RSSI

CC1020 has a built-in RSSI (Received

Signal Strength Indicator) giving a digital

value that can be read form the RSSI

and adjusted for VGA gain setting

(VGA_SETTING[4:0]

the

VGA3

The digital RSSI value is ranging from 0 to

106 (7 bits).

The RSSI reading is a logarithmic

measure of the average voltage amplitude

after the digital filter in the digital part of

the IF chain:

RSSI = 4 log2(signal amplitude)

The relative power is then given by RSSI x

1.5 dB in a logarithmic scale.

The number of samples used to calculate

the average signal amplitude is controlled

by AGC_AVG[1:0] in the VGA2 register.

The RSSI update rate is given by:

[] 1

AVG

AGC

clock

filter

RSSI

where AGC_AVG[1:0] is set in the VGA2

ChBW

clock

filter

⋅

= 2

Maximum VGA gain is programmed by the

VGA_SETTING[4:0] bits. The VGA gain is

programmed in approximately 3 dB/LSB.

The RSSI measurement can be referred to

the power (absolute value) at the RF_IN

pin by using the following equation:

P = 1.5·RSSI – 3·VGA_SETTING –

RSSI_Offset [dBm]

The RSSI_Offset depends on the channel

filter bandwidth used due to different VGA

settings. Figure 14 and Figure 15 show

typical plots of RSSI reading as a function

of input power for different channel

spacings. See section 12.5 on page 33 for

list

channel

filter

bandwidths

corresponding to the various channel

spacings. Refer to Application Note AN030

CC1020/1021 RSSI for further details.

The following method can be used to

calculate the power P in dBm from the

RSSI readout values in Figure 14 and

Figure 15:

P = 1.5·[RSSI – RSSI_ref] + P_ref

where P is the output power in dBm for the

current RSSI readout value. RSSI_ref is

the RSSI readout value taken from

Figure 14 or Figure 15 for an input power

level of P_ref. Note that the RSSI reading

in decimal value changes for different

channel filter bandwidths.

The analog filter has a finite dynamic

range and is the reason why the RSSI

reading is saturated at lower channel

spacings. Higher channel spacing is

typically used for high frequency deviation

and data rates. The analog filter bandwidth

is about 160 kHz and is bypassed for high

frequency deviation and data rates and is

the reason why the RSSI reading is not

saturated for 200 kHz and 500 kHz

channel spacing in Figure 14 and Figure

15.

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