AD620_04 AD [Analog Devices], AD620_04 Datasheet - Page 18

• Manufacturer Part Number: AD620_04
• Description: Low Cost Low Power Instrumentation Amplifier
• Manufacturer: AD [Analog Devices]

AD620
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 47, Figure 48, and Figure 49. Refer to A Designer’s Guide
to Instrumentation Amplifiers (free from Analog Devices) for
more information regarding in-amp applications.
Figure 47. Ground Returns for Bias Currents with Transformer-Coupled Inputs
+ INPUT
– INPUT
R
G
AD620
–V
+V
S
S
REFERENCE
LOAD
TO POWER
GROUND
SUPPLY
V
OUT
Rev. G | Page 18 of 20
Figure 48. Ground Returns for Bias Currents with Thermocouple Inputs
Figure 49. Ground Returns for Bias Currents with AC-Coupled Inputs
100k Ω
+ INPUT
– INPUT
100k Ω
– INPUT
+ INPUT
R
G
R
G
AD620
AD620
+V
–V
S
–V
S
+V
S
S
REFERENCE
REFERENCE
LOAD
TO POWER
LOAD
GROUND
TO POWER
SUPPLY
GROUND
SUPPLY
V
OUT
V
OUT