Characterisation of a pixel readout chip for medical X-ray imaging

A pixel readout chip for medical X-ray imaging has been developed. It is to be used in a hybrid pixel detector, where it is connected to a semiconductor sensor. A single chip consists of 992 square pixels arranged in 31 columns and 32 rows. Each pixel has a side of 270 μm and comprises a preamplifier, shaper, discriminator and two counters. The readout chip operates as a photon counter. The implementation of two counters in every single pixel cell is a design solution that makes it possible to acquire two images very close in time and under different conditions. The readout chip has been characterised in the absence of a sensor by using charge injection. Results are presented on basic functionality, threshold dispersion and the capability to perform photon counting.