An on-chip charge cluster reconstruction technique in the miniVIPIC pixel readout chip for X-ray counting and timing

An on-chip algorithm for the allocation of a hit to a single pixel in the presence of charge sharing in a highly segmented pixel detector is presented. It has been developed to advance pixel detector technology for experiments with X-ray beams at a synchrotron facility. Its key elements are: activation of groups of pixels (neighborhood_active), comparisons of peak amplitudes within the active neighborhood, virtual pixels that recover composite signals, ability to create event driven strobes to control comparisons of fractional signals between neighboring pixels and finally latching of the results of these comparisons. The miniVIPIC prototype was designed in a 130 nm process, as a proof of feasibility. The chip contains an array of 32×32 100×100 μm² pixels. Analog and digital signals are exchanged between pixels, forming an extensive inter-pixel connection grid, whose routing to minimize parasistics, represented the major challenge. The design details of the chip are provided.