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Data Sheet

AD9690

Rev. B | Page 45 of 78

HALF-BAND FILTERS

The AD9690 offers four half-band filters to enable digital signal

processing of the ADC converted data. The HB1 FIR is always

enabled and cannot be bypassed. The HB2, HB3, and HB4 FIR

filters are optional and can be bypassed for higher output

sample rates.

HB4 Filter

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

an 11-tap, symmetrical, fixed-coefficient filter implementation,

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, the filter is bypassed. Table 19 and

Figure 92 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 92. 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 implementation,

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 20 and Figure 93 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 93. 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 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 21 and Figure 94 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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