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CIRCUIT060070: Differential Input to Differential Output Circuit Using a Fully-Differential Amplifier

Nivethitha D
Intellectual 320 points
Part Number: CIRCUIT060070
Other Parts Discussed in Thread: OPA810, OPA2810

HI,

Opamp used has Differential input and output

We are giving Load cell input to the differential inputs of the opamp.

Observations:

1) Output of the load cell when measured without connecting and when connected to the opamp circuit varies.

why so? there is some drop in the load cell output when connected.

what are the possible cases for this?

2)when the feedback resistors values are increased there is no drop. how does this work?

how to fix the feedback resistor value?? do you have any guidelines

  • 0
    TI__Genius 9810 points

    Hi Nivethitha,

    From the information you are providing it sounds like the FDA is having a loading effect on the load cell causing the value to drop. This might be why increasing resistance on the FDA is helping reduce this drop. You could increase the resistor values for the FDA as this would increase the input impedance being seen from the load cell. Depending on the FDA being used, the datasheet will highlight reasonable values that can be used for the feedback network. This method will increase the overall noise of the circuit which is something that must be considered. Assuming it is a loading issue, you could also buffer the outputs of the load cell and drive the FDA this way. Figure 9-15 in the OPA810 datasheet, found here, highlights this buffered input that is used to limit any loading effects. We do have the OPA2810, which is the dual option of the OPA810.

    Best Regards,

    Ignacio