Pulse coder using magnetoresistance elements having an improved z-phase signal pattern

Claim 1

A pulse coder for generating a Z-phase signal for detecting a reference position of a rotating member, comprising: a fixed member; a rotating member rotatable with respect to said fixed member; first and second magnetic patterns formed on a circumference of said rotating member, each of said magnetic patterns having strong magnetic field generating areas and weak magnetic field generating areas arranged alternately, irregularly and non-equidistantly spaced on said circumference; and first and second magnetoresistance elements corresponding to said first and second magnetic patterns, respectively, formed on said fixed member, said first and second magnetoresistance elements being electrically connected in series with one another and operably connected to a Z-phase signal detection means, said first and second magnetoresistance elements exhibiting a minimum resistance value and a maximum resistance value, respectively, when said first and second magnetic patterns of said rotating member are brought into directly facing relation with said first and second magnetoresistance elements, respectively, of said fixed member, such that when said magnetoresistance elements directly face said strong magnetic field generating areas of said magnetic patterns said magnetoresistance elements exhibit a minimum resistance value, and when directly facing said weak magnetic field generating areas of said magnetic patterns, said magnetoresistance elements exhibit a maximum resistance value, said reference position corresponding to a rotational position of said rotating member when one of said magnetoresistance elements is caused to exhibit a maximum resistance value and the other said magnetoresistance element is caused to exhibit a minimum resistance value such that the difference in resistance value between said respective first and second magnetoresistance elements is at a maximum.