Development of a timing chip prototype in 110 nm CMOS technology

Abstract: We present a readout chip prototype for future pixel detectors with timing capabilities. The prototype is intended for characterizing 4D pixel arrays with a pixel size of $100\times100~\mu \text{m}^2$, where the sensors are Low Gain Avalanche Diodes (LGADs). The long-term focus is towards a possible replacement of disks in the extended forward pixel system (TEPX) of the CMS experiment during the High Luminosity LHC (HL-LHC). The requirements for this ASIC are the incorporation of a Time to Digital Converter (TDC) within each pixel, low power consumption, and radiation tolerance up to $5\times10^{15}~n_\text{eq}\text{~cm}^{-2}$ to withstand the radiation levels in the innermost detector modules for $3000 \text{fb}^{-1}$ of the HL-LHC (in the TEPX). A prototype has been designed and produced in 110~nm CMOS technology at LFoundry and UMC with different versions of TDC structures, together with a front end circuitry to interface with the sensors. The design of the TDC will be discussed, with the test set-up for the measurements, and the first results comparing the performance of the different structures.