Patent ID: 6528783
Filing Date: 2003-03-04
Classification: G01D,G06G

Abstract:
An electronic circuit comprising a longitudinally disposed array of electromagnetic radiation (EMR) detectors, two or more correlator units, and a phase angle computing unit, the circuit enabling measurement of the relative position of a spatially periodic intensity pattern of incident EMR impinging on the array of detectors, characterised in that the pitch of the array of EMR detectors is arranged to be smaller than the pitch of the spatially periodic intensity pattern of incident EMR, each correlator unit comprises an array of capacitors connected to a buffer, each detector has an output dependent on the incident EMR impinging on that detector, the output communicated to respective one or more capacitors in each of the two or more correlator units, the capacitances of the one or more capacitors determine a correlator coefficient for that detector in relation to the respective correlator unit, the magnitude of the correlator coefficients arranged to vary periodically in the longitudinal direction along the length of the array according to a predetermined periodic weighting function, each correlator unit analog-computing the weighted sum of the respective detector outputs according to the respective predetermined periodic weighting function for that correlator unit and outputting an analog representation of this weighted sum at its respective buffer, the weighting functions of the two or more correlator units mutually offset by a predetermined phase angle, the phase angle computing unit connected to the buffers of each correlator unit, and enabling computation of the relative phase angle of the spatially periodic intensity pattern of incident EMR, and hence its relative position expressed as the relative phase angle of the pattern.