SPECTRUM1k – 75 μm Pixels Pitch IC With In-Pixel Histogramming for X-Ray Color Imaging

A new single photon-counting IC prototype called SPECTRUM1k with pixel matrix $40\times 24$ and pixel pitch $75~\mu $ m is developed by the Microelectronics Group of the AGH University of Krakow as a solution for X-ray color imaging. The chip, produced in CMOS 40nm technology, is made up of 960 individually configured pixels, each composed of an amplifier, an analog-to-digital converter, and $64\times 12$ -bit memory cells that allow one to perform in-pixel energy histogramming. Thanks to the proposed architecture working with the 200 MHz chip clock and 1 Gcps/mm2 multi energy photon intensities up-to about 23 ms exposition time is feasible ( $365~\mu $ s exposition time whenever monoenergetic photons are used only). In-pixel offsets ( ${=} 3.5$ %) and gain ( ${=} 5.8$ %) spread, the amplifier performance (Equivalent Noise Charge ${=} 95$ e-RMS) and the ADC resolution (Effective Number of Bits ${=} 5.4$ b) allow to convert the incoming photons’ energy with FWHM ${=} 3.7$ ke @134.2 keV upon $81~\mu $ W or $48~\mu $ W per pixel power consumption. In this publication, we present a description of the ASIC’s architecture as well as characterization results. The threshold dispersions, gain spread as well as noise and energy measurement performance of the SPECTRUM1k are presented.