ADF7021 datasheet(35/64 Pages) AD

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Data Sheet

ADF7021

Rev. B | Page 35 of 64

3FSK Viterbi Detector Setup

The Viterbi detector can be used for 3FSK data detection. This

is activated by setting R13_DB11 to Logic 1.

The Viterbi path memory length is programmable in steps of 4,

6, 8, or 32 bits (VITERBI_PATH_MEMORY, R13_DB[13:14]).

The path memory length should be set equal to or greater than

the maximum number of consecutive 0s in the interleaved

transmit bit stream.

The Viterbi detector also uses threshold levels to implement the

maximum likelihood detection algorithm. These thresholds are

programmable via the 3FSK/4FSK_SLICER_THRESHOLD bits

(R13_DB[4:10]).

These bits are assigned as follows:

3FSK/4FSK_SLICER_THRESHOLD =













100

Deviation

requency

Transmit F

where K is the value calculated for correlator discriminator

bandwidth.

3FSK Threshold Detector Setup

To activate threshold detection of 3FSK, R13_DB11 should be

set to Logic 0. The 3FSK/4FSK_SLICER_THRESHOLD bits

(R13_DB[4:10]) should be set as outlined in the 3FSK Viterbi

Detector Setup section.

3FSK CDR Setup

In 3FSK, a transmit preamble of at least 40 bits of continuous 1s

is recommended to ensure a maximum number of symbol

transitions for the CDR to acquire lock.

The clock and data recovery for 3FSK requires a number of

parameters in Register 13 to be set (see Table 20).

4FSK Threshold Detector Setup

The threshold for the 4FSK detector is set using the

3FSK/4FSK_SLICER_THRESHOLD bits (R13_DB[4:10]).

The threshold should be set according to

3FSK/4FSK_SLICER_THRESHOLD =













100

Deviation

Outer

4FSK

where K is the value calculated for correlator discriminator

bandwidth.

Table 20. 3FSK CDR Settings

Parameter

Recommended Setting

Purpose

PHASE_CORRECTION (R13_DB12)

Phase correction on

3FSK_CDR_THRESHOLD (R13_DB[15:21])













100

Deviation

requency

Transmit F

where K is the value calculated for

correlator discriminator bandwidth.

Sets CDR decision threshold levels

3FSK_PREAMBLE_TIME_VALIDATE (R13_DB [22:25])

1111

Preamble detector time qualifier

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