Performance of a pixel readout chip with two counters for X-ray imaging

A pixel readout chip for X-ray imaging has been developed and tested. It will he used in a hybrid pixel detector, where it is flip-chip bonded to a sensor. The sensor material can be silicon or a compound semiconductor, such as CdZnTe. A novel feature of the chip is the implementation of two counters inside each pixel cell. The chip consists of 992 pixels arranged in 31 columns and 32 rows. Each pixel size is 270 micrometer square and it consists of a preamplifier, shaper, discriminator and two counters. The circuit design with two integrated counters in each pixel cell makes it possible to acquire two images very close in time with practically no dead time in between. An externally adjustable threshold permits the discrimination of a portion of the X-ray spectrum. The detector is primarily aimed for dynamic medical X-ray imaging up to 100 frames per second. A characterization of the performance of the chip is presented and discussed.