AD9122 Analog Devices, AD9122 Datasheet - Page 41

• Manufacturer Part Number: AD9122
• Manufacturer: Analog Devices

Specifications of AD9122

• Resolution (bits): 16bit
• Dac Update Rate: 1.23GSPS
• Dac Settling Time: n/a
• Max Pos Supply (v): +3.47V
• Single-supply: No
• Dac Type: Current Out
• Dac Input Format: LVDS,Par

DATAPATH CONFIGURATION EXAMPLES
8× Interpolation Without NCO
For this example, the following parameters are given:
•
•
•
•
The desired 75 MHz of bandwidth is 75% of f
the ratio of f
width supported at f
supports the bandwidth required in this configuration.
The signal center frequency is f
signal is at baseband, the frequency shift required is also f
Choosing the third row (highlighted by the superscripted
number 2) of the Interpolation Factor column from Table 20
selects filter modes that give a center frequency of f
frequency translation of f
half-band filters are HB1, Mode 2; HB2, Mode 2; and HB3,
Mode 1. Figure 60 shows how the signal propagates through the
interpolation filters.
Because 2 × f
frequency scaled by one-half into each consecutive stage. The
output signal band spans 0.15 to 0.35 of f
fore, the output frequency supported is 60 MHz to 140 MHz,
which covers the 75 MHz bandwidth centered at 100 MHz, as
desired.
f
8× interpolation
f
f
DATA
BW
CENTER
= 75 MHz
= 100 MSPS
= 100 MHz
OUT
IN1
/f
= f
DATA
IN2
DATA
= 100/100 = 1.0. From Figure 59, the band-
and 2 × f
is 0.8, which verifies that the AD9122
DATA
. The selected modes for the three
IN2
DATA
= f
and, assuming the input
IN3
, the signal appears
HB1
HB2
HB3
Figure 60. Signal Propagation for 8× Interpolation (f
IN3
–0.5
–0.5
–0.5
(400 MHz). There-
DATA
–0.2
. In this case,
DATA
0
0
0
0
0.1
0
0
0.15
0.2
0.25
and a
1
1
0.3
0.3
0.35
DATA
0.4
2
0.5
0.5
0.5
Rev. B | Page 41 of 60
1
2
.
0.6
0.7
0.7
0.75
3
3
4
1.0
1.0
1.0
2
4
1.25
4× Interpolation with NCO
For this example, the following parameters are given:
•
•
•
•
The desired 140 MHz of bandwidth is 56% of f
in Figure 58, the value at 0.7 × f
0.8 − 2(0.7 − 0.6) = 0.6. This verifies that the AD9122 supports
a bandwidth of 60% of f
The signal center frequency is 0.7 × f
input signal is at baseband, the frequency shift required is also
0.7 × f
column in the 4× interpolation section of Table 20 selects the filter
modes that give a center frequency of f
translation. The selected modes for the three half-band filters
are HB1, Mode 1; HB2, Mode 1; and HB3, bypassed.
Because Mode 1 of HB1 was selected, the premodulation block
should be enabled. This provides f
centers the baseband input data at the center frequency of HB1.
The digital modulator can be used to provide the final frequency
translation of 0.2 × f
as desired.
The formula for calculating the FTW of the NCO is as follows:
where:
f
f
Therefore, FTW = 2
5
5
CARRIER
NCO
6
= 2 × f
1.5
1.5
1.5
f
4× interpolation
f
f
6
3
FTW
DATA
BW
CENTER
DATA
= 0.2 × f
= 140 MHz
1.75
7
7
= 250 MSPS
DATA
. Choosing the second row in the Interpolation Factor
DATA
=
= 175 MHz
0
2.0 ×
2.0 ×
2.0 ×
Modulation)
f
.
CARRIER
f
DATA
NCO
f
f
f
IN1
IN2
IN3
.
32
DATA
/10.
×
2
DATA
to place the output signal at 0.7 × f
32
, which exceeds the required 56%.
DATA
DATA
is 0.6. This is calculated as
DATA
/2 modulation, which
DATA
and, assuming the
/2 with no frequency
DATA
. As shown
AD9122
DATA
,