AD8221AR(2003) Просмотр технического описания (PDF) - Analog Devices
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AD8221AR Datasheet PDF : 20 Pages
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AD8221
RF INTERFERENCE
RF rectification is often a problem when amplifiers are used in
applications where there are strong RF signals. The disturbance
may appear as a small dc offset voltage. High frequency signals
can be filtered with a low-pass R-C network placed at the input
of the instrumentation amplifier, as shown in Figure 49. The
filter limits the input signal bandwidth according to the
following relationship:
FilterFreqDiff =
1
2πR(2CD + CC)
FilterFreqCM = 1
2πRCC
where CD ≥ 10CC.
+15V
0.1µF
10µF
CC
R
4.02kΩ
CD
R
4.02kΩ
CC
1nF
+IN
10nF
R1
499Ω
–IN
AD8221
REF
VOUT
1nF
0.1µF
10µF
–15V
Figure 49. RFI Suppression
CD affects the difference signal and CC affects the common-
mode signal. Values of R and CC should be chosen to minimize
RFI. Mismatch between the R × CC at the positive input and the
R × CC at negative input will degrade the AD8221’s CMRR. By
using a value of CD one magnitude larger than CC, the effect of
the mismatch is reduced, and hence, performance is improved.
PRECISION STRAIN GAGE
The AD8221’s low offset and high CMRR over frequency make
it an excellent candidate for bridge measurements. As shown in
Figure 50, the bridge can be directly connected to the inputs of
the amplifier.
350Ω
350Ω
350Ω
350Ω
+5V
10µF 0.1µF
+IN +
R AD8221
–
–IN
+2.5V
Figure 50. Precision Strain Gage
Rev. A | Page 16 of 20
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