AD6679 datasheet(50/81 Pages) AD

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AD6679

Data Sheet

Rev. B | Page 50 of 81

HB3 Filter

The second decimate by 2, half-band, low-pass, FIR filter (HB3)

uses an 11-tap, symmetrical, fixed coefficient filter implementa-

tion that is optimized for low power consumption. The HB3

filter is only used when complex outputs (decimate by 8 or 16)

or real outputs (decimate by 4 or 8) are enabled; otherwise, it is

bypassed. Table 22 and Figure 68 show the coefficients and

response of the HB3 filter.

Table 22. HB3 Filter Coefficients

HB3 Coefficient

Number

Normalized

Coefficient

Decimal Coefficient

(18-Bit)

C1, C11

0.006554

859

C2, C10

C3, C9

−0.050819

−6661

C4, C8

C5, C7

0.294266

38,570

0.500000

65,536

–120

–100

–80

–60

–40

–20

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

NORMALIZED FREQUENCY (× π RAD/SAMPLE)

Figure 68. HB3 Filter Response

HB2 Filter

The third decimate by 2, half-band, low-pass, FIR filter (HB2)

uses a 19-tap, symmetrical, fixed coefficient filter implementa-

tion that is optimized for low power consumption.

The HB2 filter is only used when complex or real outputs

(decimate by 4, 8, or 16) are enabled; otherwise, it is bypassed.

Table 23 and Figure 69 show the coefficients and response of

the HB2 filter.

Table 23. HB2 Filter Coefficients

HB2 Coefficient

Number

Normalized

Coefficient

Decimal Coefficient

(19-Bit)

C1, C19

0.000614

161

C2, C18

C3, C17

−0.005066

−1328

C4, C16

C5, C15

0.022179

5814

C6, C14

C7, C13

−0.073517

−19,272

C8, C12

C9, C11

0.305786

80,160

C10

0.500000

131,072

–120

–100

–80

–60

–40

–20

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

NORMALIZED FREQUENCY (× π RAD/SAMPLE)

Figure 69. HB2 Filter Response

HB1 Filter

The fourth and final decimate by 2, half-band, low-pass, FIR

filter (HB1) uses a 55-tap, symmetrical, fixed coefficient filter

implementation that is optimized for low power consumption.

The HB1 filter is always enabled and cannot be bypassed. Table 24

and Figure 70 show the coefficients and response of the HB1 filter.

Table 24. HB1 Filter Coefficients

HB1 Coefficient

Number

Normalized

Coefficient

Decimal

Coefficient (21-Bit)

C1, C55

−0.000023

−24

C2, C54

C3, C53

0.000097

102

C4, C52

C5, C51

−0.000288

−302

C6, C50

C7, C49

0.000696

730

C8, C48

C9, C47

−0.0014725

−1544

C10, C46

C11, C45

0.002827

2964

C12, C44

C13, C43

−0.005039

−5284

C14, C42

C15, C41

0.008491

8903

C16, C40

C17, C39

−0.013717

−14,383

C18, C38

C19, C37

0.021591

22,640

C20, C36

C21, C35

−0.033833

−35,476

C22, C34

C23, C33

0.054806

57,468

C24, C32

C25, C31

−0.100557

−105,442

C26, C30

C27, C29

0.316421

331,792

C28

0.500000

524,288

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