AD713
R2*
V
DD
CMOS DAC APPLICATIONS
+15V
0.1µF
C1
The AD713 is an excellent output amplifier for CMOS DACs. It
can be used to perform both two- and four-quadrant operation.
The output impedance of a DAC using an inverted R-2R ladder
approaches R for codes containing many 1s, 3R for codes
containing a single 1, and infinity for codes containing all 0s.
33pF
GAIN
ADJUST
18
20
V
R
FB
DD
1
4
OUT1
V
19
V
IN
REF
1/4
R1*
AD7545
V
OUT
AD713
2
AGND
11
0.1µF
DGND
3
ANALOG
COMMON
For example, the output resistance of the AD7545 modulates
between 11 kΩ and 33 kΩ. Therefore, with the DAC’s internal
feedback resistance of 11 kΩ, the noise gain varies from 2 to
4/3. This changing noise gain modulates the effect of the input
offset voltage of the amplifier, resulting in nonlinear DAC
amplifier performance. The AD713, with its guaranteed 1.5 mV
input offset voltage, minimizes this effect, achieving 12-bit
performance.
–15V
DB11 TO DB0
*REFER TO TABLE 5.
Figure 42. Unipolar Binary Operation
FILTER APPLICATIONS
A Programmable State Variable Filter
For the state variable or universal filter configuration of Figure 44
to function properly, DAC A1 and DAC B1 must control the
gain and Q of the filter characteristic, and DAC A2 and DAC B2
must accurately track for the simple expression of fC to be true.
This is readily accomplished using two AD7528 DACs and one
AD713 quad op amp. Capacitor C3 compensates for the effects
of op amp gain bandwidth limitations.
Figure 42 and Figure 43 show the AD713 and a 12-bit CMOS
DAC, the AD7545, configured for either a unipolar binary (two-
quadrant multiplication) or bipolar (four-quadrant multiplication)
operation. Capacitor C1 provides phase compensation, which
reduces overshoot and ringing.
Table 5. Recommended Trim Resistor Values vs. Grades for
AD7545 for VD = 5 V
This filter provides low-pass, high-pass, and band-pass outputs
and is ideally suited for applications where microprocessor
control of filter parameters is required. The programmable
range for component values shown is fC = 0 kHz to 15 kHz and
Q = 0.3 to 4.5.
Trim Resistor JN/AQ
KN/BQ
200 Ω
68 Ω
LN/CQ
100 Ω
33 Ω
GLN/GCQ
R1
R2
500 Ω
150 Ω
20 Ω
6.8 Ω
R2*
V
DD
R4
R5
20kΩ
1%
+15V
0.1µF
20kΩ
C1
33pF
1%
GAIN
ADJUST
18
20
R3
10kΩ
1%
V
R
FB
DD
1
OUT1
AGND
4
V
19
V
IN
REF
1/4
R1*
AD7545
AD713
1/4
2
V
OUT
AD713
DGND
3
11
0.1µF
12
DATA INPUT
DB11 TO DB0
ANALOG
COMMON
–15V
*REFER TO TABLE 5.
Figure 43. Bipolar Operation
Rev. F | Page 14 of 20
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