Adder : Adder circuit is a Summing Amplifier. Op-amp can be used to design a circuit whose output is the sum of several input signals. Such a circuit is called a summing amplifier or a summer. Summing amplifier can be classified as inverting & non-inverting summer depending on the input applied to inverting & non-inverting terminals respectively. Fig shows an inverting summer with two inputs. Here the output will be the linear summation of input voltages.
Here the feedback forces a virtual ground to exist at the inverting input . The output is equal to the negative weighted sum of the input voltages. The summing operation depends exclusively on the sum of the resistor ratios. Fig . shows the inverting configuration with three inputs Va, Vb, Vc depending on the relationship between the feedback resistor RF and the input resistors Ra ,Rb and Rc , the circuit can be used as either a summing amplifier, scaling amplifier, or averaging amplifier. By connecting more than one input voltages to the inverting input, the resulting circuit is the Adder.
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