A TEMPORALLY RESOLVED POSITION SENSING DEVICE FOR AUTOFOCUSING

Abstract

A position-sensing method for autofocus purpose is demonstrated, based on the triangular ranging principle applied to a photoconductive Haynes-Shockley device. This method provides a linear variation of the minority-carrier transit time in the sensor with respect to the inverse of the object distance, or to the image distance to be adjusted from the focal point. Hence it can provide a convenient autofocusing control with a fully digital signal processing circuit. The principle of the autofocus triangular ranging is justified, and its resolution is analyzed with a p-type silicon photoconductor. The result shows that our method indeed can provide a high resolution and practically low cost autofocusing device for the camera industry.