AD9744ARUZ Analog Devices Inc, AD9744ARUZ Datasheet - Page 17

• Manufacturer Part Number: AD9744ARUZ
• Description: IC DAC 14BIT 210MSPS 28-TSSOP
• Manufacturer: Analog Devices Inc
• Series: TxDAC®r

Specifications of AD9744ARUZ

• Data Interface: Parallel
• Settling Time: 11ns
• Number Of Bits: 14
• Number Of Converters: 1
• Voltage Supply Source: Analog and Digital
• Power Dissipation (max): 145mW
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-TSSOP
• Resolution (bits): 14bit
• Sampling Rate: 210MSPS
• Input Channel Type: Parallel
• Supply Voltage Range - Analog: 2.7V To 3.6V
• Supply Voltage Range - Digital: 2.7V To 3.6V
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: AD9744ACP-PCBZ - BOARD EVAL FOR AD9744ACP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

APPLYING THE AD9744
Output Configurations
The following sections illustrate some typical output configura-
tions for the AD9744. Unless otherwise noted, it is assumed that
I
optimum dynamic performance, a differential output configu-
ration is suggested. A differential output configuration may
consist of either an RF transformer or a differential op amp
configuration. The transformer configuration provides the
optimum high frequency performance and is recommended for
any application that allows ac coupling. The differential op amp
configuration is suitable for applications requiring dc coupling,
a bipolar output, signal gain, and/or level shifting within the
bandwidth of the chosen op amp.
A single-ended output is suitable for applications requiring a
unipolar voltage output. A positive unipolar output voltage
results if IOUTA and/or IOUTB are connected to an appro-
priately sized load resistor, R
configuration may be more suitable for a single-supply system
requiring a dc-coupled, ground referred output voltage. Alter-
natively, an amplifier could be configured as an I-V converter,
thus converting IOUTA or IOUTB into a negative unipolar
voltage. This configuration provides the best dc linearity since
IOUTA or IOUTB is maintained at a virtual ground.
DIFFERENTIAL COUPLING USING A TRANS-
FORMER
An RF transformer can be used to perform a differential-to-
single-ended signal conversion, as shown in Figure 34. A
differentially coupled transformer output provides the optimum
distortion performance for output signals whose spectral con-
tent lies within the transformer’s pass band. An RF transformer,
such as the Mini-Circuits T1–1T, provides excellent rejection of
common-mode distortion (that is, even-order harmonics) and
noise over a wide frequency range. It also provides electrical
isolation and the ability to deliver twice the power to the load.
Transformers with different impedance ratios may also be used
OUTFS
11
10
9
8
7
6
5
4
3
2
1
0
is set to a nominal 20 mA. For applications requiring the
0
PECL
Figure 33. I
50
SE
DIFF
CLKVDD
100
f
CLOCK
LOAD
vs. f
(MSPS)
CLOCK
, referred to ACOM. This
150
and Clock Mode
200
250
Rev. B | Page 17 of 32
for impedance matching purposes. Note that the transformer
provides ac coupling only.
The center tap on the primary side of the transformer must be
connected to ACOM to provide the necessary dc current path
for both IOUTA and IOUTB. The complementary voltages ap-
pearing at IOUTA and IOUTB (that is, V
symmetrically around ACOM and should be maintained with
the specified output compliance range of the AD9744. A differ-
ential resistor, R
output of the transformer is connected to the load, R
passive reconstruction filter or cable. R
transformer’s impedance ratio and provides the proper source
termination that results in a low VSWR. Note that approxi-
mately half the signal power will be dissipated across R
DIFFERENTIAL COUPLING USING AN OP AMP
An op amp can also be used to perform a differential-to-
single-ended conversion, as shown in Figure 35. The AD9744 is
configured with two equal load resistors, R
differential voltage developed across IOUTA and IOUTB is
converted to a single-ended signal via the differential op amp
configuration. An optional capacitor can be installed across
IOUTA and IOUTB, forming a real pole in a low-pass filter. The
addition of this capacitor also enhances the op amp’s distortion
performance by preventing the DAC’s high slewing output from
overloading the op amp’s input.
The common-mode rejection of this configuration is typically
determined by the resistor matching. In this circuit, the differ-
ential op amp circuit using the AD8047 is configured to provide
some additional signal gain. The op amp must operate off a dual
supply since its output is approximately ±1 V. A high speed am-
plifier capable of preserving the differential performance of the
AD9744 while meeting other system level objectives (such as,
cost or power) should be selected. The op amp’s differential
gain, gain setting resistor values, and full-scale output swing
AD9744
Figure 35. DC Differential Coupling Using an Op Amp
IOUTA
IOUTB
Figure 34. Differential Output Using a Transformer
AD9744
IOUTA
IOUTB
DIFF
22
21
, may be inserted in applications where the
25Ω
22
21
C
OPT
OPTIONAL R
25Ω
MINI-CIRCUITS
225Ω
225Ω
T1-1T
DIFF
DIFF
OUTA
is determined by the
LOAD
500Ω
and V
, of 25 Ω. The
AD8047
R
500Ω
LOAD
OUTB
AD9744
LOAD
DIFF
) swing
, via a
.