ADF7021 datasheet(32/64 Pages) AD

32 / 64 page

ADF7021

Data Sheet

Rev. B | Page 32 of 64

RSSI Formula (Converting to dBm)

The RSSI formula is

Input Power [dBm] =

−130 dBm + (Readback Code + Gain Mode Correction) × 0.5

where:

Readback Code is given by Bit RV7 to Bit RV1 in the readback

Gain Mode Correction is given by the values in Table 15.

The LNA gain (LG2, LG1) and filter gain (FG2, FG1) values

are also obtained from the readback register, as part of an RSSI

readback.

Table 15. Gain Mode Correction

LNA Gain

(LG2, LG1)

Filter Gain

(FG2, FG1)

Gain Mode

Correction

H (1, 0)

M (0, 1)

H (1, 0)

M (0, 1)

L (0, 0)

An additional factor should be introduced to account for losses

in the front-end-matching network/antenna.

DEMODULATION, DETECTION, AND CDR

System Overview

An overview of the demodulation, detection, and clock and

data recovery (CDR) of the received signal on the ADF7021 is

shown in Figure 46.

The quadrature outputs of the IF filter are first limited and

then fed to either the correlator FSK demodulator or the

linear FSK demodulator. The correlator demodulator is used

to demodulate 2FSK, 3FSK, and 4FSK. The linear demodulator

is used for frequency measurement and is enabled when the

AFC loop is active. The linear demodulator can also be used

to demodulate 2FSK.

Following the demodulator, a digital post demodulator filter

removes excess noise from the demodulator signal output.

Threshold/slicer detection is used for data recovery of 2FSK and

4FSK. Data recovery of 3FSK can be implemented using either

threshold detection or Viterbi detection.

An on-chip CDR PLL is used to resynchronize the received bit

stream to a local clock. It outputs the retimed data and clock on

the TxRxDATA and TxRxCLK pins, respectively.

LIMITERS

VITERBI

DETECTION

MUX

CLOCK

AND

DATA

RECOVERY

TxRxDATA

TxRx CLK

FREQUENCY

CORRELATOR

LINEAR

DEMODULATOR

MUX

3FSK

THRESHOLD

DETECTION

2/3/4FSK

Figure 46. Overview of Demodulation, Detection, and CDR Process

Correlator Demodulator

The correlator demodulator can be used for 2FSK, 3FSK, and

4FSK demodulation. Figure 47 shows the operation of the

correlator demodulator for 2FSK.

IF –

fDEV

IF +

fDEV

LIMITERS

R4_DB(10:19)

R4_DB7

DOT/CROSS PRODUCT

FREQUENCY CORRELATOR

DISCRIMINATOR BW

R4_DB9

Rx DATA INVERT

DISCRIM BW

2FSK = +1, –1

3FSK = +1, 0, –1

4FSK = +3, +1, –1, –3

OUTPUT LEVELS:

Figure 47. 2FSK Correlator Demodulator Operation

The quadrature outputs of the IF filter are first limited and then

fed to a digital frequency correlator that performs filtering and

frequency discrimination of the 2FSK/3FSK/4FSK spectrum.

For 2FSK modulation, data is recovered by comparing the

output levels from two correlators. The performance of this

frequency discriminator approximates that of a matched filter

detector, which is known to provide optimum detection in the

presence of additive white Gaussian noise (AWGN). This

method of FSK demodulation provides approximately 3 dB to

4 dB better sensitivity than a linear demodulator.

ADF7021 Datasheet(PDF) 32 Page - Analog Devices

ADF7021 Datasheet(HTML) 32 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64

Datasheet Download

Link URL