A front-end channel in 65 nm CMOS for pixel detectors at the HL-LHC experiment upgrades

A front-end channel prototype for pixel detectors has been designed for the upgrades of the HL-LHC experiments. The circuit is based on a Krummenacher feedback network to continuously reset the charge sensitive amplifier and on a fast threshold discriminator to implement a time-over-threshold (ToT) method and perform amplitude measurement. The front-end circuit was developed in a 65 nm CMOS technology and takes an overall area not exceeding 1250 $\mu m^{2}$, i.e., half of the overall pixel area. The current consumption per channel is around 4 $\mu$A at VDD = 1.2 V. A very small charge sensitivity dispersion was detected in the set of characterized samples. An equivalent noise charge of 120 $e^{-}$ was found for a detector capacitance of 100 fF. The response of the channel is compatible with the speed requirements of the foreseen application in the innermost layers of the CMS pixel detector.