Datasheet

AD620
Rev. H | Page 17 of 20
GROUND RETURNS FOR INPUT BIAS CURRENTS
V
OUT
– INPUT
+ INPUT
R
G
LOAD
TO POWER
SUPPLY
GROUND
REFERENCE
+V
S
–V
S
AD620
00775-0-050
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 46, Figure 47, and Figure 48. Refer to A Designer’s Guide
to Instrumentation Amplifiers (free from Analog Devices) for
more information regarding in-amp applications.
V
OUT
AD620
– INPUT
R
G
TO POWER
SUPPLY
GROUND
REFERENCE
+ INPUT
+V
S
–V
S
LOAD
00775-0-049
Figure 47. Ground Returns for Bias Currents with Thermocouple Inputs
100k Ω
V
OUT
AD620
– INPUT
+ INPUT
R
G
LOAD
TO POWER
SUPPLY
GROUND
REFERENCE
100k Ω
–V
S
+V
S
00775-0-051
Figure 46. Ground Returns for Bias Currents with Transformer-Coupled Inputs
Figure 48. Ground Returns for Bias Currents with AC-Coupled Inputs