4.3 SUMMER

In a summer, or summing amplifier, many inputs are given and the output is taken from the op-amp. If the inputs are given to the inverting input, then the configuration is an inverting summing amplifier. If the inputs are given to the noninverting input, then the configuration is a non-inverting summing amplifier.

Figure 4.6: Inverting Summer.

By applying the superposition theorem, it is easy to understand the operation of this circuit.

Assuming the effect due to input V ₁, the output V _o1 can be written as

(4.18)

Similarly the output V _o2, due to input V ₂, can be written as

(4.19)

Similarly, the output V _on, due to input V _n, can be written as

(4.20)

The total output V ₀ of the system is the sum of the outputs due to individual inputs.

Substitute from equations (4.18), (4.19) and (4.20):

or

(4.21)

As a special case, if R ₁ = R ₂ =...= R _n = R, then

(4.22)

which is the sum of all inputs, multiplied by .

(4.23)

which is the sum of all input voltages.

(4.24)

where the output is the average of all input voltages.