A new CMOS optical sensor for active optical tracking is presented. The tracking function is carried out pointing the target with a collimated light beam and estimating the position of the back-reflected beam portion impinging on the device. The core of the device, fabricated in standard 0.8 /spl mu/m CMOS technology, is an array of 20 /spl times/ 20 pixels where mixed analogue-digital image pre-processing, at pixel and array level, is performed. Image contour is extracted by means of distributed peak-detection, implemented at pixel level, followed by a digital extraction of the beam centroid position executed at row and column level. The image position can be estimated in 120 /spl mu/s with an accuracy of 0.9 /spl mu/m. The chip exhibits a worst case power consumption of 15mW @ 5V and 3000 frames/s.