Asynchronous Approximation of a Center of Gravity for Pixel Detectors' Readout Circuits

This paper presents an implementation of asynchronous approximation of a center of gravity of a binary object on a focal plane of a pixel detector. The direct field of its application is dealing with charge sharing in processing of signals from semiconductor X-ray hybrid pixel detectors. The developed algorithm is called the center of gravity in a temporal object (COGITO), standing for approximation of a geometrical COGITO that is a charge cloud sampled by a pixel detector. Its operation resembles image processing for finding a center of gravity of a binary object in an image. The presented circuitry operates entirely in the digital domain-the analog pixel front end is not included. Thus, this paper does not show a complete, self-consistent solution to X-ray or particle detectors. The key details of the concept and its implementation, followed by measurements obtained with a test chip designed in a 55-nm CMOS process, are presented. The algorithm can deal with arbitrarily large objects and allocation of a hit to a single pixel can be achieved in a few tens of nanoseconds.