Validation of CMOS Active Pixel Sensor with double readout rolling shutter architecture for charged particle tracking

Abstract

Rolling shutter readout is a classical architecture in CMOS Active Pixel Sensors (APS) usually well suited to reduce the power consumption in the active area of the sensor by activating only one row at a time for reset and readout operations. Its benefits are widely used from imaging sensors to high energy physics sensors where large sensing area and low power consumptions are an issue. In the field of high-energy physics and more specifically, answering the tracking requirements of the future ALICE Muon Forward Tracker (MFT), the rolling shutter readout system has been studied and improved to overcome the limitations of the classical readout speed, by using group of two rows selected simultaneously for the reset and readout operation. As a result of this study, an ASIC prototype, named M22THRB2, has been designed in a 0.18 µm quadruple-well CMOS Image Sensor (CIS) process to assess this architecture proposal. Laboratory tests have been performed on both the in-pixel analog signal processing part and on the analogue to digital converter part of the chip. Test results on pixel noise and analog response to X-ray source are presented in details. Pixels connected to discriminators (analog+digital parts of the chip) are also characterized in laboratory giving a complete system characterization on noise distribution, fake hit rate and pixels response uniformity.