An asynchronous front-end channel 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 circuit was developed in a 65 nm CMOS technology and takes an overall area not exceeding 25 μm×50 μm. The power dissipation per channel, not including dynamic consumption, is around 5 μW. This paper is in particular concerned with the characterization of the charge sensitive amplifier, whose gain and recovery time can be adjusted to comply with changes in the experiment parameters. A very small gain dispersion was detected in the set of characterized samples. An equivalent noise charge of 120 electrons was found for a detector emulating capacitance of 100 fF. The response of the amplifier is compatible with the speed requirements for the foreseen application.