Datasheet
AD8270
Rev. 0 | Page 17 of 20
The AD8270 Specifications section and Typical Performance
Characteristics
section show the performance of the part primarily
when it is in the difference amplifier configuration. To get a good
estimate of the performance of the part in a single-ended
configuration, refer to the difference amplifier configuration
with the corresponding closed-loop gain (see
Table 9 ).
Table 9. Closed-Loop Gain of the Difference Amplifiers
Difference Amplifier Gain Closed-Loop Gain
0.5 1.5
1 2
2 3
Gain of 1 Configuration
The AD8270 is designed to be stable for loop gains of 1.5 and
greater. Because a typical voltage follower configuration has
a loop gain of 1, it may be unstable. Several stable G = 1 configu-
rations are listed in
Table 8.
DIFFERENTIAL OUTPUT
The AD8270 can easily be configured for differential output.
Figure 48 shows the configuration for a G = 1 differential output
amplifier. The OCM node in the figure sets the common-mode
output voltage.
Figure 49 shows the configuration for a G = 1
differential output amplifier, where the average of two voltages
sets the common-mode output voltage. For example, this
configuration can be used to set the common mode at 2.5 V,
using just a 5 V reference and GND.
06979-062
–IN
+IN
–
IN
+
IN
AD8270
_
+
_
+
10kΩ 10kΩ 10kΩ 10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
20kΩ 20kΩ20kΩ20kΩ
5
8
16
15
14
13
6
7
1
2
3
4
11
12
10
9
–
OUT+OUT
OCM
OCM
–OUT
+OUT
–IN
+IN
V
OCM
=
V
+IN
– V
–IN
= V
+OUT
– V
–OUT
V
OCM
= V
+OUT
+ V
–OUT
Figure 48. Differential Output, G = 1, Common-Mode Output Voltage
Set with Reference Voltage
06979-063
–IN
+IN
–
IN
+
IN
AD8270
_
+
_
+
10kΩ 10kΩ 10kΩ 10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
20kΩ 20kΩ20kΩ20kΩ
5
8
16
15
14
13
6
7
AA
1
2
3
4
11
12
10
9
–
OUT+OUT
B
–OUT
+OUT
–IN
+IN
V
OCM
=
V
+IN
– V
–IN
= V
+OUT
– V
–OUT
V
+OUT
+ V
–OUT
=
V
A
+ V
B
2
V
A
+ V
B
2
Figure 49. Differential Output, G = 1, Common-Mode Output Voltage
Set as the Average of Two Voltages
Note that these two configurations are based on the G = 0.5
difference amplifier configurations shown in
Figure 42 and
Figure 45. A similar technique can be used to create differential
output with a gain of 2 or 4, using the G = 1 and G = 2 difference
amplifier configurations, respectively.