Configurable Quadrant Photodetector: An Improved Position Sensitive Device

Position sensitive detectors (PSDs), used in high-end biotechnology, are based on optical sensors built over quadrant photodetectors (QPDs) or active pixel sensor (APS). These devices are intended to measure slight movements of laser spots. The QPD are, by far, the best approach in terms of resolution and noise, but requires complex and expensive x-y micropositioners to perform sensor alignment with the incoming laser spot. The APSs are more versatile devices that can virtually align with the spot by means of device configuration. However, due to its intrisic digital nature, the SNR and the resolutions are degraded in APS. In this paper, a new type of device called configurable QPD and its theory of operation is presented. This new device combines the analog operation of the QPD with the configurability of the APS, by means of combining photodetectors elements with analog switches in a matrix-shaped architecture. Finally, a prototype chip has been fabricated and tested and its measurements results are presented.