AD9748ACP-PCB Analog Devices Inc, AD9748ACP-PCB Datasheet - Page 15

• Manufacturer Part Number: AD9748ACP-PCB
• Description: BOARD EVAL FOR AD9748ACP
• Manufacturer: Analog Devices Inc
• Series: TxDAC®r

Specifications of AD9748ACP-PCB

• Rohs Status: RoHS non-compliant
• Number Of Dac's: 1
• Number Of Bits: 8
• Outputs And Type: 1, Differential
• Sampling Rate (per Second): 210M
• Data Interface: Parallel
• Settling Time: 11ns
• Dac Type: Current
• Voltage Supply Source: Analog and Digital
• Operating Temperature: -40°C ~ 85°C
• Utilized Ic / Part: AD9748

APPLYING THE AD9748
Output Configurations
The following sections illustrate some typical output
configurations for the AD9748. Unless otherwise noted, it is
assumed that I
requiring the optimum dynamic performance, a differential
output configuration is suggested. 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 that allows ac coupling. The
differential op amp configuration is suitable for applications
requiring dc coupling, 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 is connected to an appropriately
sized load resistor, R
can 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
converting IOUTA or IOUTB into a negative unipolar voltage.
This configuration provides the best dc linearity because
IOUTA or IOUTB is maintained at a virtual ground.
OUTFS
is set to a nominal 20 mA. For applications
LOAD
, referred to ACOM. This configuration
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DIFFERENTIAL COUPLING USING A TRANSFORMER
An RF transformer can be used to perform a differential-to-
single-ended signal conversion, as shown in Figure 25. A
differentially coupled transformer output provides the optimum
distortion performance for output signals whose spectral
content 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 can 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 (that is, V
swing symmetrically around ACOM and should be maintained
with the specified output compliance range of the AD9748. A
differential resistor, R
the output of the transformer is connected to the load, R
via a passive reconstruction filter or cable. R
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 is dissipated across R
Figure 25. Differential Output Using a Transformer
AD9748
IOUTA
IOUTB
DIFF
, can be inserted in applications where
OPTIONAL R
MINI-CIRCUITS
T1-1T
DIFF
OUTA
DIFF
is determined
and V
R
LOAD
AD9748
OUTB
DIFF
LOAD
.
)
B
,