AD9856
Figure 24 describes the input timing for half word mode, burst
input timing operation.
Figure 25 describes the input timing for quarter word, 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>.
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 half word mode, when the third half-
band filter is engaged, is given by:
The input sample rate for quarter word mode, when the third
half-band filter is engaged, is given by:
f
IN = SYSCLK/2N
fIN = SYSCLK/N
where N is the CIC interpolation rate.
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:
Please note that Half-Band Filter #3 must be engaged when operat-
ing in quarter word mode.
f
IN = SYSCLK/N
where N is the CIC interpolation rate.
TxENABLE
D(11:0)
INTERNAL I
INTERNAL Q
Q0
I1
Q1
I0
I2
Q2
I3
Q3
I4
Q4
I0
I1
I2
I3
Q0
Q1
Q2
Q3
Figure 22. 12-Bit Input Mode, Classic Burst Timing
TxENABLE
D(11:0)
INTERNAL I
INTERNAL Q
I0
Q0
I1
Q1
I2
Q2
I3
Q3
I2
I4
Q4
I0
I1
I3
Q0
Q1
Q2
Q3
Figure 23. 12-Bit Input Mode, Alternate TxENABLE Timing
TxENABLE
D(11:6)
INTERNAL I
INTERNAL Q
I0(11:6)
Q0(5:0)
Q0(11:6)
I1(11:6)
I1(5:0)
Q1(11:6)
Q1(5:0)
I2(11:6)
I2(5:0)
I1
I0(5:0)
I0
Q0
Q1
Figure 24. 6-Bit Input Mode, Burst Mode Timing
TxENABLE
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)
I0
D(11:9)
INTERNAL I
INTERNAL Q
Q0
Figure 25. 3-Bit Input Mode, Burst Mode Timing
–15–
REV. B
ADI [ ADI ]
