AD524B AD [Analog Devices], AD524B Datasheet - Page 13

• Manufacturer Part Number: AD524B
• Description: Precision Instrumentation Amplifier
• Manufacturer: AD [Analog Devices]

REV. E
Another method for developing the switching scheme is to use a
DAC. The AD7528 dual DAC, which acts essentially as a pair
of switched resistive attenuators having high analog linearity and
symmetrical bipolar transmission, is ideal in this application.
The multiplying DAC’s advantage is that it can handle inputs of
either polarity or zero without affecting the programmed gain.
The circuit shown uses an AD7528 to set the gain (DAC A) and
to perform a fine adjustment (DAC B).
AUTOZERO CIRCUITS
In many applications it is necessary to provide very accurate
data in high gain configurations. At room temperature the offset
effects can be nulled by the use of offset trimpots. Over the
operating temperature range, however, offset nulling becomes a
problem. The circuit of Figure 44 show a CMOS DAC operat-
ing in the bipolar mode and connected to the reference terminal
to provide software controllable offset adjustments.
(–INPUT)
G = 1000
(+INPUT)
G = 100
+INPUT
–INPUT
DAC A/DAC B
G = 10
Figure 43. Programmable Output Gain Using a DAC
RG
RG
1
2
INPUTS
13
12
16
11
1
3
2
DATA
WR
CS
PROTECTION
PROTECTION
4.44k
404
40
14
15
16
18
4
7
6
+V
DB0
DB7
S
17
AD7528
DAC A
DAC B
V
5
b
20k
20k
3
20k
20k
AD524
19
20
2
1
AD712
20k
20k
1/2
256:1
AD712
10
1/2
9
6
V
OUT
–13–
In many applications complex software algorithms for autozero
applications are not available. For those applications Figure 45
provides a hardware solution.
INPUTS
DATA
–V
15
ZERO PULSE
WR
CS
S
GND
V
V
DD
AD589
SS
16
14
13
MSB
LSB
39k
200 s
Figure 44. Software Controllable Offset
RG
RG
+INPUT
–INPUT
2
AD7524
1
G = 1000
Figure 45. Autozero Circuit
A1
G = 100
+V
G = 10
RG
GND
RG
S
2
V
REF
1
AD524
+V
–V
A2
8
S
S
OUT1
OUT2
AD711
C1
10
AD524
A3
0.1 F LOW
LEAKAGE
+V
–V
S
S
AD712
+V
1/2
S
A4
1k
10k
AD7510KD
12
R4
5k
R6
11
AD524
R3
20k
9
10
AD712
–V
20k
1/2
S
R5
V
OUT
CH