Preliminary Technical Data

AD8226

Rev. PrA | Page 11 of 16

AD8226

+IN

–IN

LOAD

REF

0.1µF

10µF

0.1µF

10µF

Figure 6. Supply Decoupling, REF, and Output Referred to Local Ground

References

The output voltage of the AD8226 is developed with respect to

the potential on the reference terminal. Care should be taken to

tie REF to the appropriate local ground.

INPUT BIAS CURRENT RETURN PATH

The input bias current of the AD8226 must have a return path

to ground. When the source, such as a thermocouple, cannot

provide a return current path, one should be created, as shown

in Figure 7.

THERMOCOUPLE

REF

AD8226

CAPACITIVELY COUPLED

REF

C

C

AD8226

TRANSFORMER

REF

AD8226

INCORRECT

CAPACITIVELY COUPLED

REF

C

R

R

C

AD8226

1

THERMOCOUPLE

REF

10MΩ

AD8226

TRANSFORMER

REF

AD8226

CORRECT

RADIO FREQUENCY INTERFERENCE (RFI)

RF rectification is often a problem when amplifiers are used in

applications having strong RF signals. The disturbance can appear

as a small dc offset voltage. High frequency signals can be filtered

with a low-pass RC network placed at the input of the instru-

mentation amplifier, as shown in Figure 8. The filter limits the

input signal bandwidth, according to the following relationship:

)

2

(

π

2

1

C

D

C

C

R

+

C

RC

π

2

1

R

R

AD8226

+IN

–IN

0.1µF

10µF

10µF

0.1µF

REF

10nF

1nF

1nF

4.02kΩ

4.02kΩ

Figure 8. RFI Suppression

at the negative input degrades the CMRR of the AD8226. By using

mismatch is reduced, and performance is improved.