AD8273

Rev. B | Page 12 of 16

THEORY OF OPERATION

The AD8273 has two channels, each consisting of a high

precision, low distortion op amp and four trimmed resistors.

Although such a circuit can be built discretely, placing the

resistors on the chip offers advantages to board designers that

include better dc specifications, better ac specification, and

lower production costs.

The resistors on the AD8273 are laser trimmed and tightly

matched. Specifications that depend on the resistor matching,

such as gain drift, common-mode rejection, and gain accuracy,

are better than can be achieved with standard discrete resistors.

The positive and negative input terminals of the AD8273 op amp

are not pinned out intentionally. Keeping these nodes internal

means their capacitance is considerably lower than it would be

in discrete designs. Lower capacitance at these nodes means

better loop stability and improved common-mode rejection vs.

frequency.

The internal resistors of the AD8273 lower production costs.

One part rather than several is placed on the board, which

improves both board build time and reliability.

CONFIGURATIONS

The AD8273 can be configured in several different ways; see

Figure 39 to Figure 46. Because these configurations rely on the

internal, matched resistors, these configurations have excellent

gain accuracy and gain drift.

POWER SUPPLIES

Use a stable dc voltage to power the AD8273. Noise on the

supply pins can adversely affect performance. Place a bypass

capacitor of 0.1 μF between each supply pin and ground, as

close to each pin as possible. Also, use a tantalum capacitor of

10 μF between each supply and ground. It can be farther away

from the AD8273 and typically can be shared by other precision

integrated circuits.

The AD8273 is specified at ±15 V, but it can be used with

The difference between the two supplies must be kept below 36 V.

12k

Ω

2

3

12

14

13

6k

Ω

12k

Ω

6k

Ω

–IN1

OUT1

+IN1

12k

Ω

6

5

10

8

9

6k

Ω

12k

Ω

6k

Ω

–IN2

OUT2

+IN2

Figure 39. Difference Amplifier, G = ½

6k

Ω

3

2

14

13

12k

Ω

6k

Ω

12k

Ω

–IN1

OUT1

+IN1

6k

Ω

6

5

10

8

9

12k

Ω

6k

Ω

12k

Ω

–IN2

OUT2

+IN2

12

Figure 40. Difference Amplifier, G = 2

12k

Ω

2

3

12

14

13

6k

Ω

12k

Ω

6k

Ω

IN1

OUT1

5

8

12k

Ω

6k

Ω

12k

Ω

610

9

6k

Ω

IN2

OUT2

Figure 41. Inverting Amplifier, G = ½

6k

Ω

2

3

12

14

13

12k

Ω

6k

Ω

12k

Ω

IN1

OUT1

5

8

6k

Ω

12k

Ω

6k

Ω

6

10

9

12k

Ω

IN2

OUT2

Figure 42. Inverting Amplifier, G = 2