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.

–IN

+IN

–IN

+IN

AD8270

_

+

_

+

10kΩ

10kΩ

10kΩ

10kΩ

10kΩ

10kΩ

10kΩ

10kΩ

10kΩ

10kΩ

20kΩ

20kΩ

20kΩ

20kΩ

5

8

16

15

14

13

6

7

1

2

3

4

11

12

10

9

–OUT

+OUT

OCM

OCM

–OUT

+OUT

–IN

+IN

=

Figure 48. Differential Output, G = 1, Common-Mode Output Voltage

Set with Reference Voltage

–IN

+IN

–IN

+IN

AD8270

_

+

_

+

10kΩ

10kΩ

10kΩ

10kΩ

10kΩ

10kΩ

10kΩ

10kΩ

10kΩ

10kΩ

20kΩ

20kΩ

20kΩ

20kΩ

5

8

16

15

14

13

6

7

A

A

1

2

3

4

11

12

10

9

–OUT

+OUT

B

–OUT

+OUT

–IN

+IN

=

2

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.