3.4 : Sum and Difference OpAmps

Operational amplifiers (op-amps) are versatile devices that extend beyond amplification. In this context, two specific op-amp configurations are explored: the summing and difference amplifiers.

A summing amplifier, or an adder, utilizes an op-amp to merge multiple input signals into a single output signal. When audio signals are introduced into its input channels, the input resistors initiate currents that traverse feedback resistors, resulting in an output voltage. Applying Kirchhoff's current law and Ohm's Law, the output voltage becomes a weighted sum of the input signals. This basic differential op-amp circuit plays a role in mitigating audio track noise in audio mixer applications.

Conversely, a difference amplifier, often called a subtractor, amplifies the disparity between two input signals. Two equations are established by applying Kirchhoff's current law at the inverting and non-inverting nodes. An output voltage expression is derived when equal voltages exist across both nodes. However, specific resistance ratio conditions must be satisfied for the difference amplifier to nullify common signals between the inputs. When the resistances in the corresponding branches are equal, the difference amplifier functions as a subtractor.

In summary, operational amplifiers offer amplification and the ability to perform addition and subtraction tasks. The summing amplifier combines inputs into a weighted sum. The difference amplifier amplifies the disparity between two inputs and rejects common signals. Understanding these configurations opens the door to many practical applications in signal processing and circuit design.