Hi,
I have designed an instrumentation amp from two MAX4238. I join the circuit scheme in the attached figure. The objetive is to have a very small input offset voltage in order to amplify very small voltage values (microvolts).
The circuit seems to work well (I obtain the correct gain, 11) when one of the inputs is referred to the circuit ground (I fix a common mode voltage). However, it doesn't work properly when the two inputs are floatting. I obtain a gain wich is more or less the half of the expected value.
Is this normal?
I have used two resistors to connect both inputs to ground in order to provide an input bias current path. This hasn't solved the problem.
Could you please help me with this desing?
[attachmentid=349]
The resistor values are:
R1=R4=47K
R2=R3=4.7K
Input bias current path resistors: 2.2M
I have designed an instrumentation amp from two MAX4238. I join the circuit scheme in the attached figure. The objetive is to have a very small input offset voltage in order to amplify very small voltage values (microvolts).
The circuit seems to work well (I obtain the correct gain, 11) when one of the inputs is referred to the circuit ground (I fix a common mode voltage). However, it doesn't work properly when the two inputs are floatting. I obtain a gain wich is more or less the half of the expected value.
Is this normal?
I have used two resistors to connect both inputs to ground in order to provide an input bias current path. This hasn't solved the problem.
Could you please help me with this desing?
[attachmentid=349]
The resistor values are:
R1=R4=47K
R2=R3=4.7K
Input bias current path resistors: 2.2M
