Subtracting AMPLIFIER

We know that for the above configuration we have

And

Putting above values of and in following equation

.

Ignoring 1 AS Value is very large

Adder

Let’s say we have a op Amp in following configuration.

Now we have three current that are entering the negative input of op Amp. So the total current can be written as

So here we can have three voltages, which will be multiplied by the gain, So taking direct result from previous derivations

Note that the our adder circuit is much more like the inverting feedback circuit. . Using the above example we can write individual equations for all R1 and R2 and R3 and than to find the total Vo or out put we can add them.

Writing Equation for R1 and V1

Writing Equation for R2 and V2

Writing Equation for R3 and V3

Now total (output) will be equal to the added sum of due to R1 and v1 and due to R2 and v2 and due to R3 and v3

Plugging in values from equation 6, equation 7 and equation 8