Analog Devices AD620 - Manual (Page 15)

AD620
REV. E –15–
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
V
OUT
AD620
– INPUT
R G
TO POWER
SUPPLY
GROUND
REFERENCE + INPUT
+V S
–V S
LOAD
Figure 42a. Ground Returns for Bias Currents with
Transformer Coupled Inputs
sources such as transformers, or ac-coupled sources, there must
be a dc path from each input to ground as shown in Figure 42.
Refer to the Instrumentation Amplifier Application Guide (free
from Analog Devices) for more information regarding in amp
applications.
V
OUT
– INPUT
+ INPUT
R
G
LOAD
TO POWER
SUPPLY
GROUND
REFERENCE
+V
S
–V S
AD620
Figure 42b. Ground Returns for Bias Currents with
Thermocouple Inputs
100k ⍀
V OUT
AD620
– INPUT
+ INPUT
R
G
LOAD
TO POWER
SUPPLY
GROUND
REFERENCE
100k ⍀ –V S
+V S
Figure 42c. Ground Returns for Bias Currents with AC Coupled Inputs