AD9772AASTZ Analog Devices Inc, AD9772AASTZ Datasheet - Page 26

• Manufacturer Part Number: AD9772AASTZ
• Description: IC DAC 14BIT 160MSPS 48-LQFP
• Manufacturer: Analog Devices Inc
• Series: TxDAC+®r

Specifications of AD9772AASTZ

• Data Interface: Parallel
• Settling Time: 11ns
• Number Of Bits: 14
• Number Of Converters: 1
• Voltage Supply Source: Analog and Digital
• Power Dissipation (max): 272mW
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 48-LQFP
• Resolution (bits): 14bit
• Sampling Rate: 160MSPS
• Input Channel Type: Parallel
• Supply Voltage Range - Analog: 3.1V To 3.5V
• Supply Current: 37mA
• Digital Ic Case Style: QFP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: AD9772A-EB - BOARD EVAL FOR AD9772A
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

AD9772A
APPLYING THE AD9772A
OUTPUT CONFIGURATIONS
The following sections illustrate some typical output
configurations for the AD9772A. Unless otherwise noted, it is
assumed that I
performance. For applications requiring the optimum dynamic
performance, a differential output configuration can 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
allowing ac coupling. The differential op amp configuration is
suitable for applications requiring dc coupling, a bipolar output,
signal gain, and/or level shifting.
A single-ended output is suitable for applications requiring a
unipolar voltage output. A positive unipolar output voltage
results if I
sized load resistor, R
may be more suitable for a single-supply system requiring a dc-
coupled, ground-referred output voltage. Alternatively, an amplifier
can be configured as an I-V converter, thus converting I
I
provides the best dc linearity because I
maintained at a virtual ground.
DIFFERENTIAL COUPLING USING A TRANSFORMER
An RF transformer can be used as shown in Figure 47 to perform a
differential-to-single-ended signal conversion. A differentially
coupled transformer output provides the optimum distortion
performance for output signals whose spectral content lies within
the pass band of the transformer. 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 can also be used for impedance
matching purposes. Note that the transformer provides ac coupling
only, and its linearity performance degrades at the low end of its
frequency range due to core saturation.
The center tap on the primary side of the transformer must be
connected to ACOM to provide the necessary dc current path
for both I
at I
around ACOM and should be maintained with the specified
output compliance range of the AD9772A. A differential
resistor, R
output of the transformer is connected to the load, R
OUTB
OUTA
B
into a negative unipolar voltage. This configuration
and I
OUTA
OUTA
DIFF
AD9772A
Figure 47. Differential Output Using a Transformer
OUTB
, can be inserted into applications in which the
and I
and/or I
OUTFS
I
I
OUTA
OUTB
(that is, V
OUTB
is set to a nominal 20 mA for optimum
LOAD
OUTB
. The complementary voltages appearing
B
, referred to ACOM. This configuration
B
is connected to an appropriately
OPTIONAL
R
OUTA
DIFF
and V
MINI-CIRCUITS
OUTB
OUTA
T1-1T
) swing symmetrically
or I
OUTB
R
B
LOAD
is
LOAD
OUTA
, via a
or
Rev. C | Page 26 of 40
passive reconstruction filter or cable. R
transformer’s impedance ratio and provides the proper source
termination, resulting in a low voltage standing wave ratio
(VSWR). Note that approximately half the signal power is
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 48. The AD9772A is
configured with two equal load resistors, R
differential voltage developed across I
a single-ended signal via the differential op amp configuration. An
optional capacitor can be installed across I
real pole in a low-pass filter. The addition of this capacitor also
enhances the distortion performance of the op amp by preventing
the DAC’s high slewing output from overloading the op amp input.
The common-mode rejection of this configuration is typically
determined by the resistor matching. In this circuit, the differential
op amp circuit using the AD8055 is configured to provide some
additional signal gain. The op amp must operate from a dual
supply because its output is approximately ±1.0 V. A high speed
amplifier capable of preserving the differential performance of
the AD9772A while meeting other system-level objectives (such
as cost and power) should be selected. The op amp’s differential
gain, gain-setting resistor values, and full-scale output swing
capabilities should be considered when optimizing this circuit.
The differential circuit shown in Figure 49 provides the
necessary level shifting required in a single-supply system. In
this case, AVDD, the positive analog supply for both the
AD9772A and the op amp, is also used to level-shift the
differential output of the AD9772A to midsupply (that is,
AVDD/2). The AD8057 is a suitable op amp for this application.
SINGLE-ENDED, UNBUFFERED VOLTAGE OUTPUT
Figure 50 shows the AD9772A configured to provide a unipolar
output range of approximately 0 V to 0.5 V for a doubly termi-
nated 50 Ω cable because the nominal full-scale current, I
AD9772A
Figure 49. Single-Supply DC Differential Coupled Circuit
Figure 48. DC Differential Coupling Using an Op Amp
AD9772A
I
I
OUTA
OUTB
I
I
OUTA
OUTB
DIFF
25Ω
.
25Ω
C
OPT
C
OPT
25Ω
225Ω
225Ω
25Ω
OUTA
225Ω
225Ω
DIFF
and I
OUTA
1kΩ
LOAD
AD8057
is determined by the
500Ω
500Ω
, each of 25 Ω. The
and I
OUTB
AD8055
1kΩ
500Ω
is converted to
OUTB
, forming a
AVDD
OUTFS
,