ADF7021

Preliminary Technical Data

Rev. PrI | Page 32 of 44

REGISTER 4—DEMODULATOR SETUP REGISTER

DISCRIMINATOR BW

POST DEMODULATOR BW

DEMOD

SCHEME

Rx

INVERT

IF B/W

ADDRESS

BITS

DS1

0

1

0

1

0

1

0

1

DEMODULATOR SCHEME

2FSK LINEAR DEMODULATOR

2FSK CORRELATOR/DEMODULATOR

3FSK DEMODULATOR

4FSK DEMODULATOR

RESERVED

RESERVED

RESERVED

RESERVED

DP1

0

1

PRODUCT

CROSS PRODUCT

DOT PRODUCT

RI1

0

1

0

1

INVERT

NORMAL

INVERT CLK

INVERT DATA

INVERT CLK/DATA

IFB1

0

1

0

1

IF FILTER

B/W

12kHz

18kHz

25kHz

INVALID

DS2

DS3

0

0

1

1

0

0

1

1

0

0

0

0

1

1

1

1

0

0

1

1

RI2

IFB2

0

0

1

1

Figure 36.

Register 4—Demodulator Setup Register Comments

•

Discriminator_BW =

3

10

400

_

×

× K

CLK

DEMOD

where:

[Hz]

10

100

3

Deviation

Frequency

K

×

=

Maximum value = 660.

•

RX_INVERT(R4_DB[8:9]) and DOT_PRODUCT (R4_DB7) need to be set as outlined below in order to optimize the correlator

demodulator. K is calculated using the previous formula and then rounded to the nearest integer.

K

K/2

Dot Product (R4_DB7)

Rx Invert (R4_DB[8:9])

Even

Even

0

00

Even

Odd

0

10

K

(K + 1)/2

Dot Product (R4_DB7)

Rx Invert (R4_DB[8:9])

Odd

Even

1

00

Odd

Odd

1

10

•

CLK

DEMOD

F

_BW

Post_Demod

CUTOFF

_

π

2

11

×

×

=