AD6653 datasheet(34/80 Pages) AD

34 / 80 page

AD6653

Rev. 0 | Page 34 of 80

Table 16. FIR Filter Coefficients

Coefficient

Number

Normalized

Coefficient

Decimal Coefficient

(21-Bit)

C0, C65

0.0001826

383

C1, C64

0.0006824

1431

C2, C63

0.0009298

1950

C3, C62

0.0000458

C4, C61

−0.0012689

−2661

C5, C60

−0.0008345

−1750

C6, C59

0.0011806

2476

C7, C58

0.0011387

2388

C8, C57

−0.0018439

−3867

C9, C56

−0.0024557

−5150

C10, C55

0.0018063

3788

C11, C54

0.0035825

7513

C12, C53

−0.0021510

−4511

C13, C52

−0.0056810

−11914

C14, C51

0.0017405

3650

C15, C50

0.0078602

16484

C16, C49

−0.0013437

−2818

C17, C48

−0.0110626

−23200

C18, C47

−0.0000229

−48

C19, C46

0.0146618

30748

C20, C45

0.0018959

3976

C21, C44

−0.0195594

−41019

C22, C43

−0.0053153

−11147

C23, C42

0.0255623

53608

C24, C41

0.0104036

21818

C25, C40

−0.0341468

−71611

C26, C39

−0.0192165

−40300

C27, C38

0.0471258

98830

C28, C37

0.0354118

74264

C29, C36

−0.0728111

−152696

C30, C35

−0.0768890

−161248

C31, C34

0.1607208

337056

C32, C33

0.4396725

922060

SYNCHRONIZATION

The AD6653 half-band filters within a single part or across

multiple parts can be synchronized using the external SYNC

input. Bit 5 and Bit 6 of Register 0x100 allow the half-bands to

be resynchronized on every SYNC signal or only on the first

SYNC signal after the register is written. A valid SYNC causes

the half-band filter to restart at the programmed decimation

phase value.

COMBINED FILTER PERFORMANCE

The combined response of the half-band filter and the FIR filter

is shown in Figure 72. The act of bandlimiting the ADC data

with the half-band filter ideally provides a 3 dB improvement in

the SNR at the expense of the sample rate and available

bandwidth of the output data. As a consequence of finite math,

additional quantization noise is added to the system due to

truncation in the NCO and half-band. As a consequence of the

digital filter rejection of out-of-band noise (assuming no

quantization in the filters and with a white noise floor from the

ADC), there should be a 3.16 dB improvement in the ADC

SNR. However, the added quantization lessens improvement to

about 2.66 dB.

–110

–100

–90

–80

–70

–60

–50

–40

–30

–20

–10

0.1

0.2

0.3

0.4

FRACTION OF INPUT SAMPLE RATE

Figure 72. Half-Band Filter and FIR Filter Composite Response

FINAL NCO

The output of the 32-bit fine tuning NCO is complex and

typically centered in frequency around dc. This complex output

is carried through the stages of the half-band and FIR filters to

provide proper antialiasing filtering. The final NCO provides a

means to move this complex output signal away from dc so that

a real output can be provided from the AD6653. The final NCO,

if enabled, translates the output from dc to a frequency equal to

the ADC sampling frequency divided by 8 (fADC/8). This provides

the user a decimated output signal centered at fADC/8 in frequency.

Optionally, this final NCO can be bypassed, and the dc-centered

I and Q values can be output in an interleaved fashion.

AD6653 Datasheet(PDF) 34 Page - Analog Devices

AD6653 Datasheet(HTML) 34 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 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80

Datasheet Download

Link URL