A grounding brush for mitigating static electric charge on a motor shaft includes a plurality of filaments secured to an annular frame around the shaft, with tips of the filaments disposed in a channel defined by the frame. Calibration occurs by setting respective I and Q inputs to the multipliers to zero and adjusting corresponding variable offset voltages to null the modulated carrier output. A gate of a transistor is formed at least partially below the surface of the substrate and a photodiode is adjacent to the gate.