AD9684 datasheet(43/65 Pages) AD

43 / 65 page

AD9684

Data Sheet

HB1 Filter

The fourth and final decimate by 2, half-band, low-pass FIR

filter (HB1) uses a 21-bit, symmetrical, fixed coefficient filter

implementation that is optimized for low power consumption.

The HB1 filter is always enabled and cannot be bypassed. Table 21

and Figure 65 show the coefficients and response of the HB1

filter.

Table 21. HB1 Filter Coefficients

HB1 Coefficient Number

Decimal Coefficient (21-Bit)

C1, C55

−24

C2, C54

C3, C53

102

C4, C52

C5, C51

−302

C6, C50

C7, C49

730

C8, C48

C9, C47

−1544

C10, C46

C11, C45

2964

C12, C44

C13, C43

−5284

C14, C42

C15, C41

8903

C16, C40

C17, C39

−14,383

C18, C38

C19, C37

22,640

C20, C36

C21, C35

−35,476

C22, C34

C23, C33

57,468

C24, C32

C25, C31

−105,442

C26, C30

C27, C29

331,792

C28

524,288

–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 65. HB1 Filter Response

DDC GAIN STAGE

Each DDC contains an independently controlled gain stage.

The gain is selectable as either 0 dB or 6 dB. When mixing a real

input signal down to baseband, it is recommended to enable the

6 dB gain to recenter the dynamic range of the signal within the

full scale of the output bits.

When mixing a complex input signal down to baseband, the

mixer has already recentered the dynamic range of the signal

within the full scale of the output bits and no additional gain is

necessary. However, the optional 6 dB gain compensates for low

signal strengths. The downsample by 2 portion of the HB1 FIR

filter is bypassed when using the complex to real conversion

stage (see Figure 66).

DDC COMPLEX TO REAL CONVERSION BLOCK

Each DDC contains an independently controlled complex to

real conversion block. The complex to real conversion block

reuses the last filter (HB1 FIR) in the filtering stage, along with

an fS/4 complex mixer to upconvert the signal.

After upconverting the signal, the Q portion of the complex

mixer is no longer needed and is dropped.

Figure 66 shows a simplified block diagram of the complex to

real conversion.

Rev. 0 | Page 42 of 64

AD9684 Datasheet(PDF) 43 Page - Analog Devices

AD9684 Datasheet(HTML) 43 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

Datasheet Download

Link URL