Electrical Engineering ⇒ Topic : Inverting mode

Inverting mode

Figure (a) shows the summing amplifier in inverting mode. In this case, output is a linear summation of a number of input signals. Ideal OP Amp is taken for simple analysis. Virtual ground exists at the inverting input. The input current to the ideal amplifier is zero

                          .............. (1)

                       figure (a) Summing amplifier (inverting mode).

                    .......... (2)

                             ............... (3)

In this case, the circuit is also known as weighted or scaling amplifier.

If R₁ = R₂ =..... = R_n, = R (say), Eq. (3) reduces to

                                ............... (4)

So, in this case, output is proportional to the sum of inputs.

If R/R_f = n, Eq. (4) can be written as:

                                 ............... (5)

In this case, the circuit also acts as an averaging circuit.