AD8224ACPZ-R7 datasheet(23/27 Pages) AD

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Preliminary Technical Data

AD8224

FilterFreq

DIFF = 2πRC

FilterFreq

CM = 2πRC

+15V

FilterFreq

CM = 2πR(CC + C

G )

Mismatched CC capacitors result in mismatched low-pass filters.

The imbalance causes the AD8224 to treat what would have

been a common-mode signal as a differential signal. To reduce

the effect of mismatched external CC capacitors, select a value of

CD greater than 10 times CC. This sets the differential filter

frequency lower than the common-mode frequency.

+15V

AD8224

–VS

REF

–VS

+IN

–IN

0.1µF

10µF

0.1µF

10µF

AD8224

+IN

–IN

0.1µF

10µF

0.1µF

REF

VOUT

–15V

10nF

1nF

4.02kΩ

Figure 62. RFI Suppression

COMMON-MODE INPUT VOLTAGE RANGE

VOUT

–15V

Figure 61. RFI Filtering Without External Capacitors

To eliminate high frequency common-mode signals while using

smaller source resistors, a low-pass R-C network can be placed

at the input of the instrumentation amplifier (see Figure 62).

The filter limits the input signal bandwidth according to the

following relationship:

FilterFreq

DIFF = 2πR(2 CD + CC + C

G )

The three op amp architecture of the AD8224 applies gain and

then removes the common-mode voltage. Therefore, internal

nodes in the AD8224 experience a combination of both the

gained signal and the common-mode signal. This combined

signal can be limited by the voltage supplies even when the

individual input and output signals are not. Figure 26, Figure 27,

Figure 28, and Figure 29 show the allowable common-mode

input voltage ranges for various output voltages, supply voltages,

and gains.

Rev. PrB | Page 23 of 27

AD8224ACPZ-R7 Datasheet(PDF) 23 Page - Analog Devices

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