Systems and methods for generating reference voltages are provided. The processor is configured to receive a brain signal from the brain monitoring element and a cardiac signal from the cardiac monitoring element. The analog MSM characteristic of the OI is bypassed by differential two-beam signal processing, wherein the intensity difference of two synchronous light beams is transformed in two parallel OI’s into two electrical signals that compensate in a central node. Further, two resistors are used for estimating a non-linear voltage, so as to compensate the reference voltage. If the higher resonance is provided by a monopole, the monopole is disposed radially adjacent to the helical element and is capacitively connected with the helical element through an opening in the sheath. When the eliminator selection is picked, one of the other selections is eliminated, and the remaining selections are available to be picked.