Instrumentation amplifier input

Discussion in 'The Projects Forum' started by KAS, Jan 18, 2005.

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  1. KAS

    Thread Starter Member

    Jan 18, 2005

    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?

    The resistor values are:
    Input bias current path resistors: 2.2M
  2. Dave

    Retired Moderator

    Nov 17, 2003
    Duplicate Thread. Please post replies to this topic here.

    Thank you.
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