How to superimpose 2 signals to test op amp circuit noise inmunity
The following circuit is an inverting op-amp summation amplifier. Plug the two signals you want to combine into the In1 and In2 inputs. The grounding of the non-inverting (+) input to the op-amp, and the feedback configuration ensures that the inverting (-) input to the op-amp is virtually at ground, so that the two inputs should not affect one another in any noticeable way -- only the output of the op-amp will have a combined signal.



simulate this circuit &ndash; Schematic created using CircuitLab