The Timepix4 analog front-end design: Lessons learnt on fundamental limits to noise and time resolution in highly segmented hybrid pixel detectors
R. Ballabriga, J. Alozy, F. Bandi, G. Blaj, M. Campbell, P. Christodoulou, V. Coco, Ana Dorda, S. Emiliani, K. Heijhoff, E. Heijne, Thomas Hofmann, J. Kaplon, A. Koukab, I. Kremastiotis, X. Llopart, M. Noy, A. Paternò, Markus Piller, J.M. Sallesse, V. Sriskaran, Pavel Tlustoš, M. van Beuzekom
Abstract
This manuscript describes the optimization of the front-end readout electronics for high granularity hybrid pixel detectors. The theoretical study aims at minimizing the noise and jitter. The model presented here is validated with both circuit post layout simulations and measurements on the Timepix4 Application Specific Integrated Circuit (ASIC). The analog front-end circuit and the procedure to optimize the dimensions of the main transistors are described with detail. The Timepix4 is the most recent ASIC designed in the framework of the Medipix4 Collaboration. It was manufactured in 65 nm CMOS process, and consists of a four side buttable matrix of 448 × 512 pixels with 55 µm pitch. The analog front-end has a gain of ∼36 mV/ke- when configured in High Gain Mode, and ∼20 mV/ke- when configured in Low Gain Mode. The Equivalent Noise Charge (ENC) is ∼68 e- rms and ∼80 e- rms in High Gain Mode and in Low Gain Mode respectively. In event driven mode the incoming hits can be time stamped within a ∼ 200 ps time bin and the chip can deal with a maximum flux of ∼ 3.6 MHz mm−2 s−1. In photon counting mode, the chip can deal with up to ∼ 5 GHz mm−2 s−1. The routine designed to optimize the Timepix4 front-end is then used to analyze the performance limits in terms of jitter and noise for Charge Sensitive Amplifiers in pixel detectors.