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Differential mode amplifier with one input tied to ground.

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mrinalmani

mrinalmani

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I have a current sense resistor whose one terminal is ground itself.
But the resistor is in a noisy area so I have used differential routing.
I was wondering whether differential mode amplification will be of any good for suppressing noise and ground bounce. Please note that one of the input of the differential amplifier is ground itself.
Does the circuit below make some practical sense?

Thanks!
Capture1.PNG

- - - Updated - - -

There's a small mistake, the + and - terminals of the opamp must be interchanged.
 

Well R20 & R21 are in parallel so R21 is essentially not there. In an ideal case there is still no current going through R20, although in application it will help balance the offset from the input bias current. You want the feedback going to the negative input so if you switch the pins you're now left with a regular inverting op amp configuration.

Can you explain more about the differential routing from the current sense resistor?
 

To see the advantage of a differential amplifier, redraw the schematic using a 4-terminal (thevenin) shunt resistor symbol with separate sense connection. Connecting R20 to a ground symbol confuses the differential amplifier function.
 

I appears to me that the circuit would make sense if the sensor's local ground bounced higher than the op-amp's local ground ie. VEE
But if the sensor ground goes below the op-amp ground, things could be bad.
 

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