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Difference integral

The following figure shows the configuration of op-amp as a difference (differential) integrator. Here inputs are two currents I1 and I2.


Let us assume that the inverting terminal of op-amp is at potential 'V'. Due to virtual ground concept the non-inverting terminal also appears to be at same potential 'V'
The current I1 flows through the feedback capacitance C because input current to op-amp is zero.

Taking integration on both the sides, we get,

At non-inverting terminal we can have,

Substituting this V in above output equation, we get,

Thus output is integral of difference of two input currents I1 and I2. Thus acts as difference integrator.