CMOS APS with in-pixel discrimination and improved rolling shutter architecture for charged particle tracking

The tradeoff between readout speed, granularity, power consumption, material budget and radiation hardness has balanced in favor of CMOS Active Pixel Sensor (APS) technology for the pixel detector of the incoming ALICE Muon Forward Tracker experiment. In order to avoid pile-up effects in HL-LHC, the classical rolling shutter readout system of CMOS APS, dedicated to charged particle tracking, should be improved to overcome the readout speed limit induced by the row by row signal processing. The proposed solution is based on a novel pixel design including the sensing diode, the analogue signal amplification, a correlated double sampling circuit and an auto-zeroed differential discriminator, all within a 25 μm pitch square pixel. The resulting Rolling Shutter Binary Pixel architecture (RSBPix) allows more than two rows being readout simultaneously. This paper presents a RSBPix prototype designed and fabricated in a 0.18 μm CMOS Image Sensor process. A description of the ASIC architecture is provided, followed by the detailed test results from laboratory measurements. First achievements of a low temporal and fixed pattern noise, fast readout speed (160 ns per row) digital pixel are shown.