AD8275

Rev. A | Page 11 of 16

THEORY OF OPERATION

The AD8275 level translates ±10 V signals at its inputs to 4 V

at its output. It does this by attenuating the input signal by 5.

A subtractor network performs the attenuation, the level shifting,

and the differential-to-single-ended conversion. One benefit of

the subtractor topology is that it can accept input signals

beyond its supply voltage. The subtractor is composed of tightly

matched resistors. By integrating the resistors and trimming the

resistor ratios, the AD8275 achieves 80 dB CMRR and 0.024%

gain error.

INPUT

ESD

REF2

OUT

SENSE

50k

Ω

7k

Ω

7k

Ω

50k

Ω

20k

Ω

20k

Ω

10k

Ω

2.5V

–IN

+IN

INPUT

ESD

REF1

Figure 31. AD8275 Simplified Schematic

To achieve a wider input voltage range, the AD8275 uses an

shown in Figure 31. The resistors help to set the common mode

of the internal amplifier. The benefit of this circuit is that it

extends the input range without causing crossover distortion

typical of amplifiers that have rail-to-rail complementary

transistor inputs. The input range of the internal op amp is

–10

–8

–6

600

400

200

0

–200

–400

–600

–4

–2

0

2

4

6

8

10

COMMON-MODE VOLTAGE (V)

Figure 32. AD8275 Does Not Have Crossover Distortion Typical of Rail-to-Rail

Input Amplifiers

The AD8275 employs a balanced, high gain, linear output stage

that adaptively generates current as required, eliminating the

dynamic errors found in other amplifiers. This is useful when

driving SAR ADCs, which can deliver kickback current into the

output of the amplifier. The result is a design that achieves low

distortion, consistent bandwidth, and high slew rate.

BASIC CONNECTION

The basic configurations for the AD8275 are shown in

Figure 33 and Figure 34. In Figure 33, REF1 and REF2 are

the output remains at 2 V.

AD8275

7

4

5

6

8

1

2

50k

Ω

0.1µF

50k

Ω

20k

Ω

20k

Ω

10k

Ω

3

+IN

–IN

REF2

REF1

+5V

OUT

SENSE

5

Figure 33. Basic Configuration 1: Shared Reference

In contrast, Figure 34 shows REF1 tied to ground and REF2

is 2.5 V.

AD8275

7

4

5

6

8

1

2

50k

Ω

0.1µF

50k

Ω

20k

Ω

20k

Ω

10k

Ω

3

+IN

–IN

REF2

REF1

+5V

OUT

SENSE

+

5

2

Figure 34. Basic Configuration 2: Split Reference