AD9684 datasheet(33/64 Pages) AD

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Data Sheet

AD9684

Rev. 0 | Page 33 of 64

cos(wt)

0°

90°

REAL

BANDWIDTH OF

INTEREST

BANDWIDTH OF

INTEREST IMAGE

DIGITAL FILTER

RESPONSE

ADC

SAMPLING

REAL

HALF-

BAND

FILTER

HB4 FIR

HALF-

BAND

FILTER

HB3 FIR

HALF-

BAND

FILTER

HB2 FIR

HALF-

BAND

FILTER

HB1 FIR

HALF-

BAND

FILTER

HB4 FIR

HALF-

BAND

FILTER

HB3 FIR

HALF-

BAND

FILTER

HB2 FIR

HALF-

BAND

FILTER

HB1 FIR

ADC

REAL INPUT—SAMPLED AT

FILTERING STAGE

4 DIGITAL HALF-BAND FILTERS

(HB4 + HB3 + HB2 + HB1)

FREQUENCY TRANSLATION STAGE (OPTIONAL)

DIGITAL MIXER + NCO FOR

fS/3 TUNING, THE FREQUENCY

TUNING WORD = ROUND ((

fS/3)/fS × 4096) = +1365 (0x555)

NCO TUNES CENTER OF

BANDWIDTH OF INTEREST

TO BASEBAND

BANDWIDTH OF

INTEREST IMAGE

(–6dB LOSS DUE TO

NCO + MIXER)

BANDWIDTH OF INTEREST

(–6dB LOSS DUE TO

NCO + MIXER)

–

fS/2

–

fS/3

–

fS/4

–

fS/8

fS/16

fS/8

fS/4

fS/3

fS/2

–

fS/16

–

fS/32

–

fS/2

–

fS/3

–

fS/4

–

fS/8

fS/16

fS/8

fS/4

fS/3

fS/2

–

fS/16

–

fS/32

–sin(wt)

12-BIT

NCO

DIGITAL FILTER

RESPONSE

REAL/I

COMPLEX

REAL

GAIN STAGE (OPTIONAL)

0dB OR 6dB GAIN

COMPLEX (I/Q) OUTPUTS

DECIMATE BY 16

GAIN STAGE (OPTIONAL)

0dB OR 6dB GAIN

REAL (I) OUTPUTS

DECIMATE BY 8

COMPLEX TO REAL

CONVERSION STAGE (OPTIONAL)

fS/4 MIXING + COMPLEX FILTER TO REMOVE Q

–

fS/8

fS/16

fS/8

–

fS/16

–

fS/32

–

fS/8

fS/16

fS/8

–

fS/16

–

fS/32

fS/16

–

fS/16

–

fS/32

6dB GAIN TO

COMPENSATE FOR

NCO + MIXER LOSS

6dB GAIN TO

COMPENSATE FOR

NCO + MIXER LOSS

DOWNSAMPLE BY 2

+6dB

Figure 59. DDC Theory of Operation Example (Real Input, Decimate by 16)

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