Speaker
Description
The UFSD group of Turin is working at the development of custom front-end electronics for the read-out of thin silicon sensors with moderate internal gain, aiming at high-precision time tagging applications. The development of specific ASIC for timing at INFN-Torino started in 2016. The first two ASIC prototypes, TOFFEE and ABACUS, have been successfully tested in our laboratories and at particle accelerator facilities. Leveraging on the know-how obtained in those two projects, a new low power front-end chip, named FAST, has been designed to reach the intrinsic 30 ps UFSD time resolution with a 6 pF sensor capacitance coupling.
Summary
The activities of the Turin Ultra Fast Silicon Detector (UFSD) group, are centered on the design and characterization of silicon sensors and the development of front-end electronics dedicated to UFSD sensor readout. The activity of the group is mainly focused on meeting the requirements of the next generation of HEP colliders: much higher luminosity will require systems able to include very strict requirements in terms of timing capabilities. The main role in this field is played by the High-Luminosity upgrade of the LHC (HL-LHC), where the new requirements include a pile-up factor of 150-200 events per bunch crossing. In this context, time tagging is one of the fundamental tools which can be exploited to distinguish events overlapping in space but separated in time by a few tens of pico-seconds: both ATLAS, with the High Granularity Timing Detector (HGTD) and CMS, with the MIP Timing Detectors (MTD), are pursuing time tagging projects with a 30 ps time resolution.
The measurement of the Time of Arrival of a particle is affected by uncertainties coming both from the sensor used to detect particles and from the readout electronics used to measure the weak signals generated by the sensor. In order to increase the time resolution, signals with high amplitudes and small rising time are key points. This requirement leads to the optimization of both silicon sensor and readout electronics. In this context, UFSD sensors are proposed as a good candidate for time measurements, due to their capability to generate signals with the properties listed above. For what concerns the contribution of the readout electronics, the slew rate and the front-end noise are mainly influencing the timing performances. In this paper, we present FAST, a 20 channels novel low power front-end electronics devoted to timing resolution with a front-end jitter lower than the intrinsic 30 ps limit of a typical 55 micron thick UFSD sensor. The design has been optimized for a 2 mW/ch power consumption and a sensor capacitance of 6 pF. Extensive simulation took into account the charge probability distribution, the sensor time resolution and the radiation damage effect at the expected fluencies for the CMS MTD upgrade. In order to map different solutions, we designed three flavors of FAST that differ in the amplification stages: all based on a resistive feedback TIA architecture, they presents different bandwidth and signal shaping approach, due to both topology and device choices.
The FAST performances are promising even for other research branches of applied physics, like particle therapy. In this field, having fast sensors with high spatial and time resolution is crucial to fulfill the requirement of future particle beam counters. An additional requirement for these clinical applications is the capability of being able to work with an input signal rate in the order of hundreds of MHz. According to accurate simulation, the novel ASIC FAST is able to meet the HEP timing requests as well the high rate single ion detection, useful for clinical applications with accelerated ions.
