AD8553 datasheet(14/20 Pages) AD

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AD8426

Preliminary Technical Data

Rev. PrD | Page 14 of 20

limiting resistors and low leakage diode clamps such as the

BAV199, the FJH1100s, or the SP720 should be used.

RADIO FREQUENCY INTERFERENCE (RFI)

RF interference is often a problem when amplifiers are used in

applications where there are strong RF signals. The precision

circuits in the AD8426 can rectify the RF signals so that they

appear as a dc offset voltage error. To avoid this rectification,

place a low-pass RC filter at the input of the instrumentation

amplifier (see Figure 13). The filter limits both the differential

and common-mode bandwidth, as shown in the following

equations:

)

(

DIFF

uency

FilterFreq





uency

FilterFreq



where CD  10 CC.

AD8426

+VS

+IN

–IN

0.1µF

10µF

0.1µF

REF

VOUT

–VS

10nF

1nF

4.02kΩ

Figure 13. RFI Suppression

CD affects the differential signal, and CC affects the common-

mode signal. Values of R and CC should be chosen to minimize

RFI. Any mismatch between the R × CC at the positive input

and the R × CC at the negative input degrades the CMRR of the

AD8426. By using a value of CD one order of magnitude larger

than CC, the effect of the mismatch is reduced, and performance

is improved.

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