Patent ID: 7460979

Claim:
A system for detecting movement of a substrate, system comprising: a first signal acquisition means for acquiring a first substantially sinusoidal signal related to the position of the substrate; a second signal acquisition means for acquiring a second substantially sinusoidal signal related to the position of the substrate that is substantially 90 degrees out of phase with the first substantially sinusoidal signal; a signal selection means for: comparing the first substantially sinusoidal signal and the second substantially sinusoidal signal, selecting the signal with the lesser instantaneous magnitude as the primary signal, selecting the signal with the greater instantaneous magnitude as the secondary signal, and producing a reference signal indicating whether the first substantially sinusoidal signal or the second substantially sinusoidal signal was selected as the primary signal; a phase angle converter means for converting the primary signal into a phase angle signal; and an angular movement detection means for: determining angular movement over time based on the value of the phase angle signal over time, and producing a corresponding angular movement signal.