Low digital interference counter for photon-counting pixel detectors

Single photon-counting pixel sensors are widely used in radiation imaging because of their energy resolving capability and high dynamic range. However, the close integration of the analog and digital circuits in the small pixel area puts critical constraints on the mixed mode circuit design. This includes the design considerations regarding the noise injection from the digital circuits into the analog part due to the digital switching. In addition, the large number of components requires a pixel circuit with low power consumption. In this paper, we address these two design constraints. An event counter architecture that decreases the digital switching and power consumption in a pixel is presented. The counter has the same dynamic range for capturing events and hardware cost as the conventionally used counters. We present design rules for adopting the counter architecture to a certain application. These rules enable the trade-off between readout accuracy from the pixel vs. the current in the digital parts of the pixel. Simulation of a case study circuit shows a reduction of digital activity by a factor seven, and a significant reduction of power consumption.