Datasheet

Data Sheet AD9704/AD9705/AD9706/AD9707
Rev. B | Page 41 of 44
DIFFERENTIAL BUFFERED OUTPUT USING AN OP
AMP
A dual op amp (see the circuit shown in Figure 90) can be used in
a differential version of the single-ended buffer shown in Figure 89.
The same R-C network is used to form a 1-pole differential,
low-pass filter to isolate the op amp inputs from the high
frequency images produced by the DAC outputs. The feedback
resistors, R
FB
, determine the peak signal swing by the following
formula:
V
OUT
= R
FB
× I
FS
The common-mode voltage of the output is determined by the
following formula:
2
OUT
MAXCM
V
VV −=
The maximum and minimum voltages out of the amplifier are,
respectively, the following:
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
+×=
B
FB
REF
MAX
R
R
VV 1
V
MIN
= V
MAX
− V
OUT
05926-201
R
S
AD9704/AD9705
AD9706/AD9707
IOUTA
OTCM
19
R
FB
V
OUT
REFIO
23
21
IOUTB
20
C
F
C
R
S
R
B
+
–
ADA4841-2
C
F
R
FB
V
OUT
R
B
+
–
ADA4841-2
Figure 90. Single-Supply Differential Buffer
EVALUATION BOARD
The AD9704/AD9705/AD9706/AD9707 evaluation board
connects to the Analog Devices DAC pattern generator (DPG)
to allow for quick evaluation. The DPG generates Analog Devices
provided and user created digital vectors that are input into the
AD9704/AD9705/AD9706/AD9707 at speed. A software suite
provided with the evaluation board allows the user to program
the registers in the product and the DPG. The AD9704/AD9705/
AD9706/AD9707 evaluation board is powered from a PC USB
port that also provides the AD9704/AD9705/AD9706/AD9707
SPI port interface.