AD9764AR Analog Devices Inc, AD9764AR Datasheet - Page 14

• Manufacturer Part Number: AD9764AR
• Description: DAC 1-CH Segment 14-Bit 28-Pin SOIC W
• Manufacturer: Analog Devices Inc
• Series: TxDAC®r

Specifications of AD9764AR

• Package: 28SOIC W
• Resolution: 14 Bit
• Conversion Rate: 125 MSPS
• Architecture: Segment
• Digital Interface Type: Parallel
• Number Of Outputs Per Chip: 1
• Output Type: Current
• Full Scale Error: ±7 %FSR
• Integral Nonlinearity Error: ±6.5 LSB
• Maximum Settling Time: 0.035(Typ) us
• Rohs Status: RoHS non-compliant
• Settling Time: 35ns
• Number Of Bits: 14
• Number Of Converters: 1
• Voltage Supply Source: Analog and Digital
• Power Dissipation (max): 170mW
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-SOIC (7.5mm Width)
• For Use With: AD9764-EB - BOARD EVAL FOR AD9764
• Data Interface: -

AD9764
APPLYING THE AD9764
OUTPUT CONFIGURATIONS
The following sections illustrate some typical output configura-
tions for the AD9764. Unless otherwise noted, it is assumed
that I
ing the optimum dynamic performance, a differential output
configuration is suggested. A differential output configuration
may consist of either an RF transformer or a differential op amp
configuration. The transformer configuration provides the opti-
mum high frequency performance and is recommended for any
application allowing for 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 will
result if I
sized load resistor, R
tion may be more suitable for a single-supply system requiring a
dc coupled, ground referred output voltage. Alternatively, an
amplifier could be configured as an I-V converter, thus convert-
ing I
figuration provides the best dc linearity since I
maintained at a virtual ground. Note, I
better performance than I
DIFFERENTIAL COUPLING USING A TRANSFORMER
An RF transformer can be used to perform a differential-to-
single-ended signal conversion as shown in Figure 33. A
differentially coupled transformer output provides the optimum
distortion performance for output signals whose spectral content
lies within the transformer’s passband. An RF transformer such
as the Mini-Circuits T1-1T provides excellent rejection of com-
mon-mode distortion (i.e., 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. Trans-
formers with different impedance ratios may also be used 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 I
ing at I
metrically around ACOM and should be maintained with the
specified output compliance range of the AD9764. A differential
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
Figure 33. Differential Output Using a Transformer
OUTA
OUTFS
OUTA
OUTA
OUTA
or I
DIFF
is set to a nominal 20 mA. For applications requir-
and I
OUTB
AD9764
, may be inserted in applications in which the
and/or I
and I
I
I
OUTA
OUTB
OUTB
into a negative unipolar voltage. This con-
OUTB
LOAD
OUTB
22
21
(i.e., V
. The complementary voltages appear-
, referred to ACOM. This configura-
OUTB
is connected to an appropriately
OPTIONAL R
.
OUTA
MINI-CIRCUITS
T1-1T
and V
OUTA
DIFF
DIFF
OUTB
is determined by the
provides slightly
OUTA
) swing sym-
R
LOAD
or I
LOAD
DIFF
OUTB
, via a
.
is
–14–
DIFFERENTIAL USING AN OP AMP
An op amp can also be used to perform a differential-to-single-
ended conversion as shown in Figure 34. The AD9764 is con-
figured with two equal load resistors, R
differential voltage developed across I
verted to a single-ended signal via the differential op amp con-
figuration. An optional capacitor can be installed across I
and I
of this capacitor also enhances the op amp’s distortion perfor-
mance by preventing the DAC’s high slewing output from over-
loading 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 from a
dual supply since its output is approximately 1.0 V. A high
speed amplifier capable of preserving the differential perform-
ance of the AD9764 while meeting other system level objectives
(i.e., cost, power) should be selected. The op amps differential
gain, its gain setting resistor values and full-scale output swing
capabilities should all be considered when optimizing this circuit.
The differential circuit shown in Figure 35 provides the neces-
sary level-shifting required in a single supply system. In this
case, AVDD, which is the positive analog supply for both the
AD9764 and the op amp, is also used to level-shift the differ-
ential output of the AD9764 to midsupply (i.e., AVDD/2). The
AD8041 is a suitable op amp for this application.
SINGLE-ENDED UNBUFFERED VOLTAGE OUTPUT
Figure 36 shows the AD9764 configured to provide a unipolar
output range of approximately 0 V to +0.5 V for a doubly termi-
nated 50
20 mA flows through the equivalent R
R
I
ACOM directly or via a matching R
OUTB
Figure 35. Single-Supply DC Differential Coupled Circuit
LOAD
Figure 34. DC Differential Coupling Using an Op Amp
OUTB
. The unused output (I
AD9764
represents the equivalent load resistance seen by I
AD9764
, forming a real pole in a low-pass filter. The addition
I
I
OUTA
OUTB 21
cable since the nominal full-scale current, I
I
I
OUTA
OUTB 21
22
25
22
25
C
OPT
C
OPT
OUTA
25
225
225
25
or I
225
225
LOAD
OUTA
OUTB
LOAD
1k
. Different values of
LOAD
) can be connected to
and I
of 25 . In this case,
500
AD8041
500
, of 25
AD8047
OUTB
1k
500
is con-
OUTFS
. The
REV. B
OUTA
OUTA
AVDD
, of
or