Analog addition is actually really easy if you can tolerate noise and heat and can convert to/from representing the signal as an analog current. Using Kirchhoff

Analog addition is actually really easy if you can tolerate noise and heat and can convert to/from representing the signal as an analog current. Using Kirchhoff's Current Law, addition of N currents from current sources is achieved by joining those N wires to a shared exit wire which contains the summed current.