Patent ID: 6268721
Filing Date: 2001-07-31
Classification: G01D

Abstract:
An apparatus for detecting rotational position of a target wheel, comprising:a single differential sensor comprising a first magnetostatic element and a second magnetostatic element matched to said first magnetostatic element;magnetic field means for magnetically biasing said single differential sensor;a target wheel having a plurality of slots, said plurality of slots being arranged circumferentially in a predetermined pattern of narrow and wide slots, said target wheel being rotatively disposed in relation to said single differential sensor, said first and second magnetostatic elements being spaced circumferentially with respect to said target wheel;current source means connected with said single differential sensor for providing first and second voltages respectively from each of said first and second magnetostatic elements responsive to each slot of said plurality of slots successively passing said single differential sensor; andsignal conditioning circuit means connected with said single differential sensor for providing a voltage output responsive to said first and second voltages, wherein said output voltage is distinctively different for respective passage of said wide slots as compared to said narrow slots with respect to said single differential sensor;wherein said current source means provides matched currents to each of said first and second magnetostatic elements; and wherein said magnetic field means provides matched biasing magnetic fields to each of said first and second magnetostatic elements;wherein said signal conditioning circuit means comprises:differential amplifier means for converting said first and second voltages into a differential output signal;peak detection means for detecting a peak voltage of said differential output signal;first sampling means for sampling said first and second voltages responsive to said peak detection means detecting said peak voltage to thereby provide a sampled first voltage of said first voltage and a sampled second voltage of said second voltage;means for determining a midpoint voltage between said sampled first voltage and said sampled second voltage;zero detection means for detecting a zero voltage of said differential output signal;second sampling means for sampling at least one of said first and second voltages responsive to said zero detection means detecting said zero voltage to thereby detect a crossover voltage;comparator means for comparing said midpoint voltage to said crossover voltage, wherein said comparator means provides a comparator voltage distinctly different for passage, respectively, of said wide slots as compared to said narrow slots with respect to said single differential sensor;wherein when a narrow slot passes said single differential sensor said crossover voltage exceeds said midpoint voltage, and wherein when a wide slot passes said single differential sensor said midpoint voltage exceeds said crossover voltage.