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Data Sheet

AD6674

Rev. C | Page 51 of 96

HALF-BAND FILTERS

The AD6674 offers four half-band filters to enable digital signal

processing of the ADC converted data. These half-band filters

are bypassable and can be individually selected.

HB4 Filter

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

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

tion 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 106 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

−0.049316

−808

C4, C8

C5, C7

0.293273

4805

0.500000

8192

–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 106. HB4 Filter Response

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 20 and Figure 107 show the coefficients and

response of the HB3 filter.

Table 20. 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 107. 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) is enabled; otherwise, it is bypassed.

Table 21 and Figure 108 show the coefficients and response of

the HB2 filter.

Table 21. 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

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