Abstract
ALICE plans to replace its Inner Tracking System during the second long shut down of the LHC in 2019 with a new 10 m2 tracker constructed entirely with monolithic active pixel sensors. The TowerJazz 180 nm CMOS imaging Sensor process has been selected to produce the sensor as it offers a deep pwell allowing full CMOS in-pixel circuitry and different starting materials. First full-scale prototypes have been fabricated and tested. Radiation tolerance has also been verified. In this paper the development of the charge sensitive front end and in particular its optimization for uniformity of charge threshold and time response will be presented.
Highlights
Front end optimization for the monolithic active pixel sensor of the ALICE Inner Tracking System upgrade
The spatial resolution of 5 μm is achieved with an average cluster size of ∼ 2 pixels. These results show that the pALPIDE-2 satisfies the ALICE ITS requirements
After the circuit and transistor size optimization, from pALPIDE-2 to pALPIDE-3 the pulse duration uniformity is improved by a factor 2
Summary
The ALPIDE architecture is based on in-pixel hit discrimination and zero suppression readout by priority encoding [7]. The charge signal is integrated at the input node PIX_IN with a typical collection time of ∼ 10 ns. The PIX_IN voltage signal amplitude is equal to the ratio of the collected charge QIN to the total input capacitance CIN. The reset circuit restores the input baseline voltage level within a time of around 1 ms. It provides compensation for the sensor leakage current which is expected to be below 2 pA. The discriminated output OUT_D is put in coincidence with the STROBE signal, allowing the latching of the hit information in the multi event buffer memory. The data is readout by a hit-driven architecture that has activity only when there are stored hits
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