Op-Amp Effect of loading and Input impedance for Sensor application

Thread Starter

mishra87

Joined Jan 17, 2016
695
Hi Guys,

I wanted to know the reason, why loading effect comes into picture if restive sensor is connected with inverting op-amp while no loading effect with non inverting op-amp?

Thanks !!!
 

danadak

Joined Mar 10, 2018
4,057
1584441820238.png

In above, because of virtual ground that exists at INV input the Zin = Rin.

1584442075629.png

In above, only a very small bias current flows into/out of NINV input, so it looks like
very hi Z.

There is an effect due to freq response that in both cases affects the impedance's. Thats
an involved AC analysis, typically done with LaPlace analysis. Its a fun analysis to do as
Zin is complex as the amplifier runs out of G at higher freq.

One can use a diff amp in which Zin is high in both cases.

1584442566099.png


Regards, Dana.
 

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OBW0549

Joined Mar 2, 2015
3,304
I wanted to know the reason, why loading effect comes into picture if restive sensor is connected with inverting op-amp while no loading effect with non inverting op-amp?
With the inverting amplifier configuration, the sensor's internal resistance and the input resistor of the amplifier are in series and form a voltage divider which reduces the effective output voltage of the sensor. With the non-inverting configuration there is no voltage reduction because the amplifier's input impedance is extremely high, if not infinite.
 
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