AD6688 datasheet(55/138 Pages) AD

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Data Sheet

AD6688

Rev. 0 | Page 55 of 138

HB4 Filter Description

The first decimate by 2, half-band, low-pass, FIR filter (HB4) uses

an 11-tap, symmetrical, fixed coefficient filter implementation

that is optimized for low power consumption. The HB4 filter is

only used when complex outputs (decimate by 16) or real

outputs (decimate by 8) are enabled; otherwise, it is bypassed.

Table 19 and Figure 81 show the coefficients and response of

the HB4 filter.

Table 19. HB4 Filter Coefficients

HB4 Coefficient

Number

Normalized

Coefficient

Decimal

Coefficient (15-Bit)

C1, C11

0.006042

C2, C10

C3, C9

−0.049377

−809

C4, C8

C5, C7

0.293304

4806

0.5

8192

–160

–140

–120

–100

–80

–60

–40

–20

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

NORMALIZED FREQUENCY (× Π RAD/s)

Figure 81. HB4 Filter Response

HB3 Filter Description

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 20 and Figure 82 show the coefficients and

response of the HB3 filter.

Table 20. HB3 Filter Coefficients

HB3 Coefficient

Number

Normalized

Coefficient

Decimal Coefficient

(17-Bit)

C1, C11

0.006637

435

C2, C10

C3, C9

−0.051055

−3346

C4, C8

C5, C7

0.294418

19295

0.500000

65,536

–160

–140

–120

–100

–80

–60

–40

–20

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

NORMALIZED FREQUENCY (× Π RAD/s)

Figure 82. HB3 Filter Response

HB2 Filter Description

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) is enabled; otherwise, it is bypassed.

Table 21 and Figure 83 show the coefficients and response of

the HB2 filter.

Table 21. HB2 Filter Coefficients

HB2 Coefficient

Number

Normalized

Coefficient

Decimal

Coefficient (18-Bit)

C1, C19

0.000671

C2, C18

C3, C17

−0.005325

−698

C4, C16

C5, C15

0.022743

2981

C6, C14

C7, C13

−0.074180

−9723

C8, C12

C9, C11

0.306091

40120

C10

0.5

65536

–160

–140

–120

–100

–80

–60

–40

–20

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

NORMALIZED FREQUENCY (× Π RAD/s)

Figure 83. HB2 Filter Response

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