MightyPix at the LHCb Mighty Tracker — verification of an HV-CMOS pixel chip's digital readout

MightyPix is a high voltage complementary metal-oxide-semiconductor (HV-CMOS) active pixel sensor, currently being developed for the Mighty Tracker, an upgrade proposed for LHCb in anticipation of the High Luminosity LHC. To ensure that MightyPix will be able to handle the particle hit rates at the Mighty Tracker, which are expected to reach 17 MHz/cm$^2$, simulations of the chip's digital readout mechanism were performed. Using simulated particle hits the chip's performance within the LHCb environment is characterised. For this, a behavioural model of the first prototype, MightyPix1, representing the analogue pixel matrix, together with the synthesised digital logic is used. Simulation results show the MightyPix1 readout mechanism having an efficiency over 99 % up to 20 MHz/cm$^2$. The bottleneck was found to be the speed at which the hits are read out. This yielded new design ideas to improve the readout for MightyPix2, leading to an efficiency of over 99 % up to 30 MHz/cm$^2$.