AD9856AST datasheet(15/32 Pages) AD

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AD9856

–15–

REV. B

Figure 24 describes the input timing for half word mode, burst

input timing operation.

In half word mode, data is input on the D<11:6> inputs. The

D<5:0> inputs are unused in this mode and should be tied to

DGND or DVDD. The AD9856 expects the data to be input in

the following manner: I<11:6>,I<5:0>,Q<11:6>,Q<5:0>.

Data is twos complement, the sign bit is D<11> in notation

I<11:0>,Q<11:0>.

The input sample rate for half word mode, when the third half-

band filter is engaged, is given by:

fIN = SYSCLK/2N

where N is the CIC interpolation rate.

The input sample rate for half word mode, when the third half-

band filter is not engaged is given by:

fIN = SYSCLK/N

where N is the CIC interpolation rate.

Figure 25 describes the input timing for quarter word, burst

input timing operation.

In quarter word mode, data is input on the D<11:9> inputs.

The D<8:0> inputs are unused in this mode and should be tied

to DGND or DVDD. The AD9856 expects the data to be input

in the following manner: I<11:9>, I<8:6>, I<5:3>, I<2:0>,

Q<11:9>, Q<8:6>, Q<5:3>, Q<2:0>. Data is twos comple-

ment, the sign bit is D<11> in notation I<11:0>, Q<11:0>.

The input sample rate for quarter word mode, when the third

half-band filter is engaged, is given by:

fIN = SYSCLK/N

where N is the CIC interpolation rate.

Please note that Half-Band Filter #3 must be engaged when operat-

ing in quarter word mode.

TxENABLE

D(11:0)

INTERNAL I

INTERNAL Q

Figure 22. 12-Bit Input Mode, Classic Burst Timing

TxENABLE

D(11:0)

INTERNAL I

INTERNAL Q

Figure 23. 12-Bit Input Mode, Alternate TxENABLE Timing

TxENABLE

D(11:6)

INTERNAL I

INTERNAL Q

I0(11:6)

I0(5:0)

Q0(5:0)

I1(11:6)

I1(5:0)

Q1(11:6)

Q1(5:0)

I2(11:6)

Q0(11:6)

I2(5:0)

Figure 24. 6-Bit Input Mode, Burst Mode Timing

I0(11:9)

I0(8:6)

I0(5:3)

I0(2:0)

Q0(11:9)

Q0(8:6)

Q0(5:3)

Q0(2:0)

I1(11:9)

I1(8:6)

TxENABLE

D(11:9)

INTERNAL I

INTERNAL Q

Figure 25. 3-Bit Input Mode, Burst Mode Timing

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