Absolute rotary angular measurement by using multi electrode circular position sensitive detector

A new type or circular semiconductor position sensitive detector (PSD) called multi electrode circular PSD (MbCPSD), which consists of a photosensitive region, a résister line, and 16 electrodes, is presented. The photosensitive region is in the shape of a ring, which is formed by the radial arrangement of long and narrow photodiodes. The outer ends of the photodiodes are connected to the continuous resistor line. Photoexcited carriers generated in the photodiode flow to the resistor line and are extracted by the multi electrode, which divides the resistor into 16 equal parts. The angular position of the light spot is calculated from the output current of the selected electrodes. Compared to conventional circular PSDs, the reliability of angular measurement is better, this is because the ME-CPSD does not have an undetectable region caused by unavoidable discontinuities in the structure of conventional circular PSDs. This device can not only measure the absolute angular position but also carry out a more precise angular measurement by selecting narrower electrode intervals. This device has the capability of realizing a high-precision noncontact angular measurement system with a simple construction.