AD9122 Analog Devices, AD9122 Datasheet - Page 42

• 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

AD9122
DATA RATES vs. INTERPOLATION MODES
Table 22 summarizes the maximum bus speed (f
input data rates, and signal bandwidths with the various combi-
nations of bus width modes and interpolation rates. The real
signal bandwidth supported is a fraction of the input data rate,
which depends on the interpolation filters (HB1, HB2, or HB3)
selected. The complex signal bandwidth supported is twice the
real signal bandwidth.
In general, 2× interpolation is best supported by enabling HB1,
and 4× interpolation is best supported by enabling HB1 and HB2.
However, in some cases, power dissipation can be lowered by not
using HB1. If the bandwidth required is low enough, 2× interpo-
lation can be supported by using HB2, and 4× interpolation can
be supported by using HB2 and HB3.
COARSE MODULATION MIXING SEQUENCES
The coarse digital quadrature modulation occurs within the
interpolation filters. The modulation shifts the frequency
spectrum of the incoming data by the frequency offset selected.
The frequency offsets available are multiples of the input data
rate. The modulation is equivalent to multiplying the quadra-
ture input signal by a complex carrier signal, C(t), of the form
Table 22. Summary of Data Rates and Bandwidths vs. Interpolation Modes (DVDD18, CVDD18 = 1.9 V ± 2%)
Bus Width
Nibble (4 Bits)
Byte (8 Bits)
Word (16 Bits)
C ( t ) = cos( ω
c
t ) + j sin( ω
HB3
0
0
0
0
1
1
0
0
0
0
1
1
0
0
0
0
1
1
Filter Modes
HB2
0
0
1
1
1
1
0
0
1
1
1
1
0
0
1
1
1
1
c
t )
HB1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
f
1230
1230
1230
1230
1230
1230
1230
1230
1230
1230
1230
615
1230
1000
1230
615
615
307.5
BUS
BUS
(Mbps)
), supported
Rev. B | Page 42 of 60
f
153.75
153.75
153.75
153.75
153.75
153.75
307.5
307.5
307.5
307.5
307.5
153.75
615
500
615
307.5
307.5
153.75
DATA
(Mbps)
In practice, this modulation results in the mixing functions
shown in Table 21.
Table 21. Modulation Mixing Sequences
Modulation
f
f
3f
f
Note that
As shown in Table 21, the mixing functions of most of the modes
cross-couple samples between the I and Q channels. The I and
Q channels operate independently only in f
that real modulation using both the I and Q DAC outputs can
only be done in f
complex input data and produce complex output signals.
S
S
S
/2
/4
/8
S
/4
Real Signal Bandwidth (MHz)
75
60
37.5
60
37.5
60
150
120
75
120
75
60
300
200
150
120
75
60
r
=
2
Mixing Sequence
I = I, −I, I, −I, …
Q = Q, −Q, Q, −Q, …
I = I, Q, −I, −Q, …
Q = Q, −I, −Q, I, …
I = I, −Q, −I, Q, …
Q = Q, I, −Q, −I, …
I = I, r(I + Q), Q, r(−I + Q), −I, −r(I + Q), −Q, r(I − Q), …
Q = Q, r(Q − I), −I, −r(Q + I), −Q, r(−Q + I), I, r(Q + I), …
2
S
/2 mode. All other modulation modes require
S
/2 mode. This means
f
153.75
307.5
307.5
615
615
1230
307.5
615
615
1230
1230
1230
615
1000
1230
1230
1230
1230
DAC
(MHz)