AD622 查看數據表（PDF） - Analog Devices
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AD622 Datasheet PDF : 16 Pages
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AD622
Figure 18 shows an example where the differential filter
frequency is approximately 400 Hz, and the common-mode
filter frequency is approximately 40 kHz. With this differential
filter in place and operating at gain of 1000, the typical dc offset
shift over a frequency range of 1 Hz to 20 MHz is less than 1.5 μV
RTI, and the RF signal rejection of the circuit is better than
71 dB. At a gain of 100, the dc offset shift is well below 1 mV
RTI, and RF rejection is greater than 70 dB.
The input resistors should be selected to be high enough to
isolate the sensor from the CC and C D capacitors but low
enough not to influence system noise. Mismatch between
R × CC at the positive input and R × CC at the negative input
degrades the CMRR of the AD622. Therefore, the CC capacitors
should be high precision types such as NPO/COG ceramics.
The tolerance of the CD capacitor is less critical.
GROUND RETURNS FOR INPUT BIAS CURRENTS
Input bias currents are those currents necessary to bias the
input transistors of an amplifier. There must be a direct return
path for these currents; therefore, when amplifying floating
input sources such as transformers or ac-coupled sources, there
must be a dc path from each input to ground as shown in
Figure 19, Figure 20, and Figure 21. Refer to the Designer’s
Guide to Instrumentation Amplifiers (free from Analog Devices,
Inc.) for more information regarding in-amp applications.
–IN
2
1
RG
8
3
+IN
+VS
7
AD622
6
5
4
REF
VOUT
LOAD
–VS
TO POWER
SUPPLY
GROUND
Figure 19. Ground Returns for Bias Currents with Transformer Coupled Inputs
–IN
2
1
RG
8
3
+IN
+VS
7
AD622
6
5
4
REF
VOUT
LOAD
–VS
TO POWER
SUPPLY
GROUND
Figure 20. Ground Returns for Bias Currents with Thermocouple Inputs
+VS
–IN
2
7
1
RG
AD622
6
VOUT
100kΩ
8
3
+IN
100kΩ
5
4
REF
–VS
LOAD
TO POWER
SUPPLY
GROUND
Figure 21. Ground Returns for Bias Currents with AC-Coupled Inputs
Rev. D | Page 12 of 16
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