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AD6684

Data Sheet

Rev. 0 | Page 42 of 107

HALF-BAND FILTERS

The AD6684 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 18 and Figure 77 show the coefficients and

response of the HB4 filter.

Table 18. HB4 Filter Coefficients

HB4 Coefficient

Number

Decimal

Coefficient

Quantized

Coefficient (15-Bit)

C1, C11

0.006042

C2, C10

C3, C9

−0.049377

−809

C4, C8

C5, C7

0.293334

4806

0.500000

8192

–250

–200

–150

–100

–50

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

NORMALIZED FREQUENCY (×

RAD/SAMPLE)

Figure 77. 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 19 and Figure 78 show the coefficients and

response of the HB3 filter.

Table 19. HB3 Filter Coefficients

HB3 Coefficient

Number

Decimal

Coefficient

Quantized

Coefficient (17-Bit)

C1, C11

0.006638

435

C2, C10

C3, C9

−0.051055

−3,346

C4, C8

C5, C7

0.294418

19,295

0.500000

32,768

–180

–100

–60

–40

–20

–160

–140

–120

–80

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

NORMALIZED FREQUENCY (×

RAD/SAMPLE)

Figure 78. 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 20 and Figure 79 show the coefficients and response of

the HB2 filter.

Table 20. HB2 Filter Coefficients

HB2 Coefficient

Number

Decimal

Coefficient

Quantized

Coefficient (18-Bit)

C1, C19

0.000671

C2, C18

C3, C17

−0.005325

−698

C4, C16

C5, C15

0.022743

2,981

C6, C14

C7, C13

−0.074181

−9,723

C8, C12

C9, C11

0.306091

40,120

C10

0.500000

65,536

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