Design and characterization of a 28 nm CMOS charge sensitive amplifier for harsh radiation environments

This paper discusses the design and the characterization of a charge sensitive amplifier (CSA) for the readout of hybrid pixels detectors in harsh radiation environments. The CSA, designed in a 28 nm CMOS technology, includes a feedback network for detector leakage compensation and requires around 4 mu A for standard operation at a nominal voltage of 0.9 V. Test results show that the CSA is fully functional in the presence of a detector emulating leakage current up to 10 nA. The measured equivalent noise charge is close to 70 electrons r.m.s. for a sensor emulating capacitance of 50 fF, in the default bias settings. The Time-over-Threshold (ToT) performance of the CSA has also been investigated, with a maximum integral non-linearity of 3.8% detected in the ToT characteristic. The paper also reports the main performance parameters of the CSA exposed to X-rays, for total ionizing doses up to 1 Grad(SiO2).