AD9760ARU Analog Devices Inc, AD9760ARU Datasheet - Page 16

• Manufacturer Part Number: AD9760ARU
• Description: IC DAC 10BIT 125MSPS 28-TSSOP
• Manufacturer: Analog Devices Inc
• Series: TxDAC®r

Specifications of AD9760ARU

• Settling Time: 35ns
• Rohs Status: RoHS non-compliant
• Number Of Bits: 10
• Number Of Converters: 1
• Voltage Supply Source: Analog and Digital
• Power Dissipation (max): 175mW
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-TSSOP
• Number Of Channels: 1
• Resolution: 10b
• Interface Type: Parallel
• Single Supply Voltage (typ): 5V
• Dual Supply Voltage (typ): Not RequiredV
• Power Supply Requirement: Analog and Digital
• Output Type: Current
• Single Supply Voltage (min): 2.7V
• Single Supply Voltage (max): 5.5V
• Dual Supply Voltage (min): Not RequiredV
• Dual Supply Voltage (max): Not RequiredV
• Operating Temp Range: -40C to 85C
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 28
• For Use With: AD9760-EBZ - BOARD EVAL FOR AD9760
• Data Interface: -
• Lead Free Status / RoHS Status: Not Compliant

AD9760
APPLYING THE AD9760
OUTPUT CONFIGURATIONS
The following sections illustrate some typical output configura-
tions for the AD9760. 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 that 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 50. 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
cally around ACOM and should be maintained with the specified
output compliance range of the AD9760. A differential resistor,
R
transformer is connected to the load, R
construction 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
DIFF
Figure 50. Differential Output Using a Transformer
OUTA
OUTFS
, may be inserted in applications where the output of the
OUTA
OUTA
OUTA
or I
is set to a nominal 20 mA. For applications requir-
and I
AD9760
OUTB
and/or I
and I
OUTB
I
I
OUTA
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
.
DIFF
MINI-CIRCUITS
and V
T1-1T
is determined by the
LOAD
DIFF
OUTB
OUTA
, via a passive re-
OUTA
) swing symmetri-
provides slightly
R
LOAD
or I
DIFF
OUTB
.
is
–16–
DIFFERENTIAL USING AN OP AMP
An op amp can also be used to perform a differential to single-
ended conversion as shown in Figure 51. The AD9760 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 amps distortion perfor-
mance by preventing the DACs 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 off of a
dual supply since its output is approximately ± 1.0 V. A high
speed amplifier capable of preserving the differential perfor-
mance of the AD9760 while meeting other system level objec-
tives (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 opti-
mizing this circuit.
The differential circuit shown in Figure 52 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
AD9760 and the op amp is also used to level-shift the differ-
ential output of the AD9760 to midsupply (i.e., AVDD/2). The
AD8041 is a suitable op amp for this application.
SINGLE-ENDED UNBUFFERED VOLTAGE OUTPUT
Figure 53 shows the AD9760 configured to provide a unipolar
output range of approximately 0 V to +0.5 V for a doubly termi-
nated 50 Ω cable since the nominal full-scale current, I
20 mA flows through the equivalent R
R
I
to ACOM directly or via a matching R
OUTB
Figure 52. Single-Supply DC Differential Coupled Circuit
LOAD
Figure 51. DC Differential Coupling Using an Op Amp
OUTB
AD9760
. The unused output (I
represents the equivalent load resistance seen by I
AD9760
, forming a real pole in a low-pass filter. The addition
I
I
OUTA
OUTB
I
I
OUTA
OUTB 21
22
21
25
22
25
C
OPT
C
OPT
25
OUTA
225
225
25
or I
225
225
OUTA
LOAD
OUTB
LOAD
LOAD
1k
and I
) can be connected
. Different values of
of 25 Ω. In this case,
AD8041
, of 25 Ω. The
500
500
AD8047
OUTB
1k
500
is con-
OUTFS
REV. B
AVDD
OUTA
OUTA
, of
or