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Data Sheet

AD9684

Rev. 0 | Page 41 of 64

HALF-BAND FILTERS

The AD9684 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 15-bit, symmetrical, fixed coefficient filter implementation

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

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

(decimate by 8) are enabled; otherwise, the filter is bypassed.

Table 18 and Figure 62 show the coefficients and response of

the HB4 filter.

Table 18. HB4 Filter Coefficients

HB4 Coefficient Number

Decimal Coefficient (15-Bit)

C1, C11

C2, C10

C3, C9

−808

C4, C8

C5, C7

4805

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 62. HB4 Filter Response

HB3 Filter

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

uses an 18-bit, symmetrical, fixed coefficient filter implementation

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, the filter is

bypassed. Table 19 and Figure 63 show the coefficients and

response of the HB3 filter.

Table 19. HB3 Filter Coefficients

HB3 Coefficient Number

Decimal Coefficient (18-Bit)

C1, C11

859

C2, C10

C3, C9

−6661

C4, C8

C5, C7

38570

65536

–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 63. HB3 Filter Response

HB2 Filter

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

uses a 19-bit, symmetrical, fixed coefficient filter implementation

that is optimized for low power consumption. The HB2 filter is

only used when complex outputs (decimate by 4, 8, or 16) or

real outputs (decimate by 2, 4, or 8) are enabled; otherwise, the

filter is bypassed.

Table 20 and Figure 64 show the coefficients and response of

the HB2 filter.

Table 20. HB2 Filter Coefficients

HB2 Coefficient Number

Decimal Coefficient (19-Bit)

C1, C19

161

C2, C18

C3, C17

−1328

C4, C16

C5, C15

5814

C6, C14

C7, C13

−19272

C8, C12

C9, C11

80,160

C10

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 64. HB2 Filter Response

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