AD9754ARU Analog Devices Inc, AD9754ARU Datasheet - Page 14

• Manufacturer Part Number: AD9754ARU
• Description: IC DAC 14BIT 125MSPS 28-TSSOP
• Manufacturer: Analog Devices Inc
• Series: TxDAC®r

Specifications of AD9754ARU

• Mounting Type: Surface Mount
• Rohs Status: RoHS non-compliant
• Settling Time: 35ns
• Number Of Bits: 14
• Data Interface: Parallel
• Number Of Converters: 1
• Voltage Supply Source: Analog and Digital
• Power Dissipation (max): 220mW
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 28-TSSOP
• Resolution (bits): 14bit
• No. Of Pins: 28
• Update Rate: 125MSPS
• Peak Reflow Compatible (260 C): No
• No. Of Bits: 14 Bit
• Leaded Process Compatible: No
• Voltage Rating: 5V
• Number Of Channels: 1
• Resolution: 14b
• 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): 4.5V
• 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
• Lead Free Status / Rohs Status: Not Compliant

APPLYING THE AD9754
OUTPUT CONFIGURATIONS
The following sections illustrate some typical output configura-
tions for the AD9754. 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 IOUTA and/or IOUTB is connected to an appropri-
ately sized load resistor, R
figuration may be more suitable for a single-supply system
requiring a dc coupled, ground referred output voltage. Alterna-
tively, 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. Note, IOUTA
provides slightly better performance than IOUTB.
DIFFERENTIAL COUPLING USING A TRANSFORMER
An RF transformer can be used to perform a differential-to-
single-ended signal conversion as shown in Figure 27. 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
common-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 IOUTA and IOUTB. The complementary voltages
appearing at IOUTA and IOUTB (i.e., V
swing symmetrically around ACOM and should be maintained
with the specified output compliance range of the AD9754. A
differential resistor, R
which the output of the transformer is connected to the load,
R
mined by the transformer’s impedance ratio and provides the
proper source termination that results in a low VSWR. Note
that approximately half the signal power will be dissipated
across R
AD9754
LOAD
Figure 27. Differential Output Using a Transformer
OUTFS
, via a passive reconstruction filter or cable. R
DIFF
is set to a nominal 20 mA. For applications requir-
.
AD9754
IOUTA
IOUTB
DIFF
22
21
, may be inserted in applications in
LOAD
OPTIONAL R
, referred to ACOM. This con-
MINI-CIRCUITS
T1-1T
DIFF
OUTA
and V
R
LOAD
DIFF
OUTB
is deter-
)
–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 28. The AD9754 is con-
figured 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 dis-
tortion 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 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 such
as the AD8055 or AD9632 capable of preserving the differential
performance of the AD9754 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 opti-
mizing this circuit.
The differential circuit shown in Figure 29 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
AD9754 and the op amp, is also used to level-shift the differ-
ential output of the AD9754 to midsupply (i.e., AVDD/2). The
AD8041 is a suitable op amp for this application.
Figure 29. Single-Supply DC Differential Coupled Circuit
Figure 28. DC Differential Coupling Using an Op Amp
AD9754
IOUTA
AD9754
IOUTB
IOUTA
IOUTB
22
21
25
22
21
25
C
OPT
C
OPT
25
225
225
25
225
225
1k
LOAD
AD8041
500
500
, of 25
AD8055
1k
500
. The
REV. A
AVDD