AD9707-EBZ Analog Devices Inc, AD9707-EBZ Datasheet - Page 40

• Manufacturer Part Number: AD9707-EBZ
• Description: Eval Board 14-BIT Low Power TxDAC DAC IC
• Manufacturer: Analog Devices Inc
• Series: TxDAC®r

Specifications of AD9707-EBZ

• Number Of Dac's: 1
• Number Of Bits: 14
• Outputs And Type: 1, Differential
• Sampling Rate (per Second): 175M
• Data Interface: Serial
• Settling Time: 11ns
• Dac Type: Current
• Voltage Supply Source: Analog and Digital
• Operating Temperature: -40°C ~ 85°C
• Utilized Ic / Part: AD9707
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD9704/AD9705/AD9706/AD9707
APPLICATIONS
OUTPUT CONFIGURATIONS
The following sections illustrate some typical output
configurations for the AD9704/AD9705/AD9706/AD9707.
Unless otherwise noted, it is assumed that I
nominal 2 mA. For applications 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, signal gain,
and/or a low output impedance.
A single-ended output is suitable for applications where low
cost and low power consumption are primary concerns.
DIFFERENTIAL COUPLING USING A TRANSFORMER
An RF transformer can be used to perform a differential-to-
single-ended signal conversion, as shown in Figure 89. The
distortion performance of a transformer typically exceeds that
available from standard op amps, particularly at higher
frequencies. Transformer coupling provides excellent rejection
of common-mode distortion (that is, even-order harmonics)
over a wide frequency range. It also provides electrical isolation
and can deliver voltage gain without adding noise. Transformers
with different impedance ratios can also be used for impedance
matching purposes. The main disadvantages of transformer
coupling are the low frequency roll-off, lack of power gain, and
the higher output impedance.
The center tap on the primary side of the transformer must be
connected to a voltage that keeps the voltages on IOUTA and
IOUTB within the output common voltage range of the device.
Note that the dc component of the DAC output current is equal
to I
tap of the transformer should provide a path for this dc current.
In many applications, AGND provides the most convenient
voltage for the transformer center tap. The complementary
voltages appearing at IOUTA and IOUTB (that is, V
V
maintained with the specified output compliance range of the
AD9704/AD9705/AD9706/AD9707.
IOUTB
FS
AD9704/AD9705
AD9706/AD9707
/2 and flows out of both IOUTA and IOUTB. The center
) swing symmetrically around AGND and should be
Figure 89. Differential Output Using a Transformer
IOUTB
IOUTA
20
21
OPTIONAL R
OUTFS
DIFF
is set to a
IOUTA
R
LOAD
and
Rev. A | Page 40 of 52
A differential resistor, R
where the output of the transformer is connected to the load,
R
reflected by the transformer, is chosen to provide a source
termination that results in a low VSWR. Note that approxi-
mately half the signal power is dissipated across R
SINGLE-ENDED BUFFERED OUTPUT
USING AN OP AMP
An op amp such as the ADA4899-1 can be used to perform
a single-ended current-to-voltage conversion, as shown in
Figure 90. The AD9704/AD9705/AD9706/AD9707 are config-
ured with a pair of series resistors, R
feedback resistor, R
formula
The common-mode voltage of the output is determined by the
formula
The maximum and minimum voltages out of the amplifier are,
respectively,
LOAD
AD9704/AD9705
AD9706/AD9707
V
V
V
V
, via a passive reconstruction filter or cable. R
OUT
CM
MAX
MIN
=
=
=
=
V
V
R
V
REF
Figure 90. Single-Supply Single-Ended Buffer
FB
MAX
REF
IOUTA
IOUTB
REFIO
OTCM
×
×
×
−
I
⎛
⎜
⎜
⎝
FB
2
FS
1
⎛
⎜
⎜
⎝
I
1
21
20
, determines the peak signal swing by the
23
19
+
FS
+
R
×
DIFF
R
R
FB
R
B
R
R
FB
B
FB
, can be inserted in applications
S
⎞
⎟
⎟
⎠
R
⎞
⎟
⎟
⎠
−
S
V
OUT
R
C
B
S
, off each output. The
ADA4899-1
–
+
R
+5V
–5V
C
FB
F
DIFF
DIFF
.
, as
V
OUT