AD8226 查看數據表（PDF） - Analog Devices
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AD8226 Datasheet PDF : 28 Pages
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Data Sheet
Common-Mode Rejection Ratio Over Frequency
Poor layout can cause some of the common-mode signals to be
converted to differential signals before reaching the in-amp.
Such conversions occur when one input path has a frequency
response that is different from the other. To keep CMRR across
frequency high, the input source impedance and capacitance of
each path should be closely matched. Additional source resistance
in the input path (for example, for input protection) should be
placed close to the in-amp inputs, which minimizes their
interaction with parasitic capacitance from the PCB traces.
Parasitic capacitance at the gain-setting pins can also affect
CMRR over frequency. If the board design has a component
at the gain-setting pins (for example, a switch or jumper), the
part should be chosen so that the parasitic capacitance is as
small as possible.
Power Supplies
A stable dc voltage should be used to power the instrumentation
amplifier. Note that noise on the supply pins can adversely affect
performance. For more information, see the PSRR performance
curves in Figure 23 and Figure 24.
A 0.1 μF capacitor should be placed as close as possible to each
supply pin. As shown in Figure 61, a 10 μF tantalum capacitor
can be used farther away from the part. In most cases, it can be
shared by other precision integrated circuits.
+VS
0.1µF
+IN
AD8226
–IN
REF
10µF
VOUT
LOAD
0.1µF
10µF
–VS
Figure 61. 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.
AD8226
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 62.
INCORRECT
CORRECT
+VS
+VS
AD8226
REF
–VS
TRANSFORMER
+VS
AD8226
REF
–VS
TRANSFORMER
+VS
AD8226
REF
–VS
THERMOCOUPLE
AD8226
REF
10MΩ
–VS
THERMOCOUPLE
+VS
C
+VS
C
AD8226
fHIGH-PASS
=
1
2πRC
R
AD8226
C
REF
C
REF
R
–VS
CAPACITIVELY COUPLED
–VS
CAPACITIVELY COUPLED
Figure 62. Creating an IBIAS Path
Rev. C | Page 21 of 28
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