Datasheet

AD8236
Rev. 0 | Page 18 of 20
APPLICATIONS INFORMATION
AC-COUPLED INSTRUMENTATION AMPLIFIER
An integrator can be tied to the AD8236 in feedback to create a
high-pass filter as shown in Figure 41. This circuit can be used
to reject dc voltages and offsets. At low frequencies, the impedance
of the capacitor, C, is high. Therefore, the gain of the integrator
is high. DC voltage at the output of the AD8236 is inverted and
gained by the integrator. The inverted signal is injected back into
the REF pin, nulling the output. In contrast, at high frequencies,
the integrator has low gain because the impedance of C is low.
Voltage changes at high frequencies are inverted but at a low
gain. The signal is injected into the REF pins, but it is not enough to
null the output. At very high frequencies, the capacitor appears as
a short. The op amp is at unity gain. High frequency signals are,
therefore, allowed to pass.
When a signal exceeds f
HIGH-PASS
, the AD8236 outputs the high-
pass filtered input signal.
AD8236
AD8603
R
+
V
S
+IN
–IN
0.1µF
0.1µF
10µF
REF
C
+V
S
+V
S
V
REF
1
2RC
f
HIGH-PASS
=
08000-142
Figure 41. AC-Coupled Circuit