Please cite this article in press as: R. Bugalho, et al., Experimental results with TOFPET2 ASIC for time-of-flight applications, Nuclear Inst. and Methods in Physics Research, A (2017), https://doi.org/10.1016/j.nima.2017.11.034. Nuclear Inst. and Methods in Physics Research, A ( ) – Contents lists available at ScienceDirect Nuclear Inst. and Methods in Physics Research, A journal homepage: www.elsevier.com/locate/nima Experimental results with TOFPET2 ASIC for time-of-flight applications Ricardo Bugalho b , Agostino Di Francesco a, *, Luis Ferramacho b , Carlos Leong b , Tahereh Niknejad b , Luis Oliveira c , Luca Pacher d , Manuel Rolo d , Angelo Rivetti d , Miguel Silveira b , Jose C. Silva a, b , Rui Silva a , Stefaan Tavernier b, e , Joao Varela a, b a LIP, Lisbon, Portugal b PETsys Electronics, Oeiras, Portugal c CTS-UNINOVA, DEE FCT-UNL, Caparica, Portugal d INFN–sez. Torino, via Pietro Giuria 1, Torino, Italy e Vrije Universiteit, Bruxel, Belgium article info Keywords: Applications PET ASIC TOFPET Electronics Front-end abstract We present the experimental results obtained with TOFPET2, a readout and digitization ASIC for radiation detectors using Silicon Photomultipliers. The circuit is designed in CMOS 110 nm technology, has 64 independent channels and is optimized for time-of-flight measurement in PET or other applications. The chip has quad- buffered TDCs and charge integration ADCs in each channel. The chip tape-out was done in September 2016 and first tests started in beginning March 2017. Coincidence Time Resolution (CTR) of 164 ps FWHM has been measured with 22 Na point source. The energy resolution achieved for the 511 keV peak is 10.5% FWHM. © 2017 Elsevier B.V. All rights reserved. 1. Introduction Modern clinical PET scanners for medical imaging use time-of- flight (ToF) measurement as a procedure to improve signal-to-noise and background ratio and hence spatial resolution [1]. These scanners use 20 mm long LYSO crystals as scintillators, for detection of the back- to-back  rays, and silicon photomultipliers (SiPM) as transducers. A coincidence time resolution (CTR) of 316 ps full width at half maximum (FWHM) was measured for the Vereos clinical PET scanner [2]. A limit of 230 ps FWHM to the achievable CTR was demonstrated experimentally by [3] for 2 × 2 × 20 mm 3 LYSO crystals and 3 × 3 mm 2 SiPMs. In order to reach this value, the read out electronics contribution to CTR must be negligible. A time resolution in the order of 200 ps, as pursued by the EndoTOFPET-US project [4], would lead to a significative improvement in the medical imaging technique of ToF-PET, widening its clinical applications. This goal can be achieved with high speed amplifiers with low noise and low input impedance, sensitive to the first photons produced by the scintillator [5]. TOFPET2 is a 64 channel Application-Specific Integrated Circuit (ASIC) developed to provide a read out system for PET scanners, matching the specifications for high resolution discussed so far, aiming at a CTR better than 300 ps and allowing scalability from small animal scanners to clinical PET, without significant degradation. The ASIC * Corresponding author. E-mail address: agodifra@lip.pt (A. Di Francesco). provides a low power analog front-end and a digitization system, with the whole chip requiring a power consumption less than 10 mW per channel. The test of the ASIC started in March 2017. In this article we present first results on the TOFPET2 character- ization. After the description of the TOFPET2 architecture and the data acquisition system (DAQ) developed for the ASIC, results of first TOFPET2 tests will be presented, divided in two sections. The first section will cover the characterization of the individual subsystems of the ASIC. The second section will focus on tests for PET applications, analyzing the CTR achievable with TOFPET2 and SiPMs from several producers coupled to 3 × 3 × 5 mm 3 LYSO crystals. 2. Overview of TOFPET2 TOFPET2 provides analog readout and internal digitization of the Time of Arrival (ToA) and energy of input signals, the latter being performed either through charge integration or time over threshold. The output data is fully digital, with a communication interface working with a 320 MHz or a 400 MHz clock, which is fed to the TOFPET2 from an external source, through an LVDS link. The digitized signals are communicated in push mode to a dedicated data acquisition system (DAQ), through up to four LVDS links, each one working at a maximum https://doi.org/10.1016/j.nima.2017.11.034 Received 30 September 2017; Received in revised form 6 November 2017; Accepted 9 November 2017 Available online xxxx 0168-9002/© 2017 Elsevier B.V. All rights reserved.