AD9116-EBZ Analog Devices, AD9116-EBZ Datasheet - Page 43

• Manufacturer Part Number: AD9116-EBZ
• Description: Dual, 8-/10-/12-/14-bit Low Power Digital-to-analog Converters
• Manufacturer: Analog Devices

APPLICATIONS INFORMATION
OUTPUT CONFIGURATIONS
The following sections illustrate some typical output configu-
rations for the AD9114/AD9115/AD9116/AD9117. Unless
otherwise noted, it is assumed that I
20 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 trans-
former 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 88. 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 low frequency roll-off, lack-of-power gain, and
high output impedance.
The center tap on the primary side of the transformer must be
connected to a voltage that keeps the voltages on IOUTP and
IOUTN within the output common-mode voltage range of the
device. Note that the dc component of the DAC output current
is equal to I
center tap of the transformer should provide a path for this dc
current. In most applications, AGND provides the most conve-
nient voltage for the transformer center tap. The complementary
voltages appearing at IOUTP and IOUTN (that is, V
V
maintained with the specified output compliance range of the
AD9114/AD9115/AD9116/AD9117.
IOUTN
AD9114/AD9115/
AD9116/AD9117
) swing symmetrically around AGND and should be
Figure 88. Differential Output Using a Transformer
OUTFS
IOUTN
IOUTP
and flows out of both IOUTP and IOUTN. The
29
28
OPTIONAL R
OUTFS
is set to a nominal
DIFF
IOUTP
R
LOAD
and
Rev. 0 | Page 43 of 48
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 approx-
imately half the signal power is dissipated across R
SINGLE-ENDED BUFFERED OUTPUT USING
AN OP AMP
An op amp such as the
a single-ended current-to-voltage conversion, as shown in
Figure 89. The AD9114/AD9115/AD9116/AD9117 are config-
ured with a pair of series resistors, R
distortion performance, R
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
AD9114/AD9115/
AD9116/AD9117
V
V
V
V
, via a passive reconstruction filter or cable. R
OUT
CM
MAX
MIN
= V
FB
= R
=
=
AD9114/AD9115/AD9116/AD9117
, determines the peak-to-peak signal swing by the
V
V
REF
FB
MAX
Figure 89. Single-Supply Single-Ended Buffer
REF
IOUTP
IOUTN
REFIO
AVSS
× I
×
– I
×
FS
⎛
⎜
⎜
⎝
1
⎛
⎜ ⎜
⎝
FS
28
34
29
25
1
+
× R
+
ADA4899-1
R
DIFF
R
R
FB
R
R
FB
B
S
FB
S
B
, can be inserted in applications
should be set to 0 Ω. The feedback
R
⎞
⎟
⎟
⎠
S
⎞
⎟ ⎟
⎠
−
R
R
C
FB
B
2
×
can be used to perform
S
, off each output. For best
I
FS
ADA4899-1
–
+
+5V
–5V
R
C
FB
F
DIFF
DIFF
.
, as
V
OUT