Serial powering in four-chip prototype RD53A modules for Phase 2 upgrade of the CMS pixel detector

Serial powering is the baseline choice for the upgrade of the CMS pixel detector for the High Luminosity LHC. The first results with the four-chip prototype pixel detector modules based on the demonstrator \SI{65}{nm} CMOS technology RD53A chip are presented. The serially powered chain is operated at a constant supply current and the regulation is performed on-chip using a shunt low-dropout regulator (SLDO). Chips on each module are powered in parallel to prevent single-point failures. The SLDO behaviour in the system is presented as well as relevant differences in the behaviour compared to single chips. The noise levels are measured in pixels of a module in a serially powered chain and no increase is observed compared to a single module or the reported noise levels for a single chip.