AD524CDZ 查看數據表（PDF） - Analog Devices
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AD524CDZ Datasheet PDF : 28 Pages
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AD524
PROGRAMMABLE GAIN
Figure 47 shows the AD524 being used as a software program-
mable gain amplifier. Gain switching can be accomplished with
mechanical switches such as DIP switches or reed relays. It should
be noted that the on resistance of the switch in series with the
internal gain resistor becomes part of the gain equation and has
an effect on gain accuracy.
The AD524 can also be connected for gain in the output stage.
Figure 48 shows an AD711 used as an active attenuator in the
output amplifier’s feedback loop. The active attenuation presents
very low impedance to the feedback resistors, therefore
minimizing the common-mode rejection ratio degradation.
(+INPUT)
–IN
1
(–INPUT)
+IN
2
INPUT
OFFSET
NULL
3
4
10kΩ
5
6
–VS
7
+VS
8
1µF
35V
PROTECTION
PROTECTION
+VS
20kΩ
20kΩ 20kΩ
+–
AD524
20kΩ
16
15
14
20kΩ
20kΩ
4.44kΩ
13
404Ω
12
40Ω
11
20kΩ
10
9
OUTPUT
OFFSET
NULL
TO –V
R2
10kΩ
VOUT
10pF
VSS VDD GND
+VS
–
AD711
+
–VS
1
15
8
16
2
13
14
11
12
9
10
AD7590
34567
39.2kΩ
28.7kΩ
316kΩ
1kΩ
1kΩ
1kΩ
VDD A2 A3 A4 WR
Figure 48. Programmable Output Gain
+INPUT
(–INPUT)
1
G = 10 13
G = 100 12
G = 1000 11
RG1 16
RG2 3
PROTECTION
4.44kΩ
404Ω
40Ω
–INPUT 2 PROTECTION
(+INPUT)
AD524
Vb
20kΩ 20kΩ
20kΩ 20kΩ
20kΩ
10
9
6
20kΩ
DATA
INPUTS
CS
WR
DAC A /DAC B
+VS
17
3
4
14 DB0
DAC A
7 DB7
15
AD7528
16
6
18
DAC B
5
1/2
AD712
2
256:1
1
19
20
1/2
AD712
VOUT
Figure 49. Programmable Output Gain Using a DAC
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 trim potenti-
ometers. Over the operating temperature range, however,
offset nulling becomes a problem. The circuit of Figure 50
shows a CMOS DAC operating in bipolar mode and connected
to the reference terminal to provide software controllable offset
adjustments.
Rev. F | Page 20 of 28
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