AD9689-2000EBZ datasheet(62/134 Pages) AD

62 / 134 page

AD9689

Data Sheet

Rev. A | Page 62 of 134

DDC MIXED DECIMATION SETTINGS

The AD9689 also supports DDCs with different decimation

rates. In this scenario, the chip decimation ratio must be set to

the lowest decimation ratio of all the DDC channels. Samples of

higher decimation ratio DDCs are repeated to match the chip

decimation ratio sample rate. Only mixed decimation ratios that

are integer multiples of 2 are supported. For example, decimate

by 1, 2, 4, 8, or 16 can be mixed together; decimate by 3, 6, 12,

24, or 48 can be mixed together; or decimate by 5, 10, 20, or 40

can be mixed together.

Table 25 shows the DDC sample mapping when the chip

decimation ratio is different than the DDC decimation ratio.

For example, if the chip decimation ratio is set to decimate by 4,

DDC0 is set to use the HB2 + HB1 filters (complex outputs are

decimate by 4) and DDC1 is set to use the HB4 + HB3 + HB2 +

HB1 filters (real outputs are decimate by 8), then DDC1 repeats

its output data two times for every one DDC0 output. The

resulting output samples are shown in Table 26.

Table 25. Sample Mapping When the Chip Decimation Ratio (DCM) Does Not Match DDC DCM

Sample Index

DDC DCM = Chip DCM

DDC DCM = 2 × Chip DCM

DDC DCM = 4 × Chip DCM

DDC DCM = 8 × Chip DCM

N + 1

N + 2

N + 1

N + 3

N + 1

N + 4

N + 2

N + 1

N + 5

N + 2

N + 1

N + 6

N + 3

N + 1

N + 7

N + 3

N + 1

N + 8

N + 4

N + 2

N + 1

N + 9

N + 4

N + 2

N + 1

N + 10

N + 5

N + 2

N + 1

N + 11

N + 5

N + 2

N + 1

N + 12

N + 6

N + 3

N + 1

N + 13

N + 6

N + 3

N + 1

N + 14

N + 7

N + 3

N + 1

N + 15

N + 7

N + 3

N + 1

N + 16

N + 8

N + 4

N + 2

N + 17

N + 8

N + 4

N + 2

N + 18

N + 9

N + 4

N + 2

N + 19

N + 9

N + 4

N + 2

N + 20

N + 10

N + 5

N + 2

N + 21

N + 10

N + 5

N + 2

N + 22

N + 11

N + 5

N + 2

N + 23

N + 11

N + 5

N + 2

N + 24

N + 12

N + 6

N + 3

N + 25

N + 12

N + 6

N + 3

N + 26

N + 13

N + 6

N + 3

N + 27

N + 13

N + 6

N + 3

N + 28

N + 14

N + 7

N + 3

N + 29

N + 14

N + 7

N + 3

N + 30

N + 15

N + 7

N + 3

N + 31

N + 15

N + 7

N + 3

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