2848 IEEE TRANSACTIONS ON NUCLEAR SCIENCE, VOL. 57, NO. 5, OCTOBER 2010 Performance of the Low-Jitter High-Gain/Bandwidth Front-End Electronics of the HADES tRPC Wall Daniel Belver, P. Cabanelas, E. Castro, J. A. Garzón, A. Gil, D. Gonzalez-Diaz, W. Koenig, and M. Traxler Abstract—A front-end electronics (FEE) chain for accurate time measurements has been developed for the new Resistive Plate Chamber (RPC)-based Time-of-Flight (TOF) wall of the High Acceptance Di-Electron Spectrometer (HADES). The wall covers an area of around 8 , divided in 6 sectors. In total, 1122 4-gap timing RPC cells are read-out by 2244 time and charge sensitive channels. The FEE chain consists of 2 custom-made boards: a 4-channel DaughterBOard (DBO) and a 32-channel Mother- BOard (MBO). The DBO uses a fast 2 GHz amplifier feeding a dual high-speed discriminator. The time and charge information are encoded, respectively, in the leading edge and the width of an LVDS signal. Each MBO houses up to 8 DBOs providing them regulated voltage supply, threshold values via DACs, test signals and, additionally, routing out a signal proportional to the channel multiplicity needed for a 1st level trigger decision. The MBO delivers LVDS signals to a multi-purpose Trigger Readout Board (TRB) for data acquisition. The FEE allows achieving a system resolution around 75 ps fulfilling comfortably the requirements of the HADES upgrade [1]. The commissioning of the whole RPC wall is finished and the 6 sectors are already mounted in their final position in the HADES spectrometer and ready to take data during the beam-times fore- seen for 2010. Index Terms—Charge to width algorithm, fast amplifying and digitizing electronics, front-end electronics, HADES, time of flight, timing RPC. I. INTRODUCTION H ADES (High Acceptance Di-Electron Spectrometer) at GSI-SIS is investigating the properties of Nuclear Matter induced by p, nucleus and beams at kinetic energies in the range of 1–3.5 GeV/A [2]. In order to cope with the high par- ticle multiplicities at rates up to 700 expected for heavy nuclei systems, such as Au+Au, and for lighter nuclei systems up to 8 GeV/A as will be provided by FAIR-SIS100 (Facility for Antiproton and Ion Research) in the future, the HADES spec- trometer is being upgraded. Manuscript received March 02, 2010; revised May 11, 2010; accepted June 26, 2010. Date of publication August 23, 2010; date of current version October 15, 2010.This work was supported by the EC FP6-Hadron Physics RII3-CT- 2004-506078, EC DIRAC RII3-CT-2005-515876, EC FP7/2007-2011 under Grant 227431, MEC Grants FPA2006-09154 and FPA2006-12120-C03-02 and XUGA Grant PGIDIT06PXIC20601PM. D. Belver, P. Cabanelas, E. Castro, and J. A. Garzón are with the LabCAF, Universidad de Santiago de Compostela, 15782 Santiago de Compostela, Spain (e-mail: daniel.belver@usc.es). A. Gil is with the Instituto de Física Corpuscular (CSIC-Universidad de Va- lencia), 46071 Valencia, Spain. D. Gonzalez-Diaz, W. Koenig, and M. Traxler are with GSI Helmholtzentrum mbH, 64291 Darmstadt, Germany. Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TNS.2010.2056928 Fig. 1. One full RPC sector, showing the 187 cells distributed in 3 columns and 2 layers. RPC cells in the second layer cover the dead regions of the first one in order to ensure full acceptance. As a part of this upgrade project, an RPC wall for Particle Identification (PID) and trigger has been constructed and in- stalled. The wall consists of 6 sectors covering around 8 in the low polar angle region of HADES ( ). Each sector has 187 4-gap glass-aluminum shielded cells, distributed in 3 columns and 2 layers (see Fig. 1), with a total number of 1122 RPC cells and read by 2244 electronic channels. One more cell has been added per sector as compared to [3]. Taking into account the HADES physics performances, the inner Time-of-Flight (TOF) wall should conform to the fol- lowing parameters [3], [4]:  Area of the ToF wall .  Effective cell occupancy below 5% for lepton detection.  Rate capability up to 1 in the innermost part.  Robust multi-hit capability, implying low crosstalk.  High time resolution ( ) for separating pairs from fast pions.  High intrinsic and .  A fast, low noise and compact FEE design. The most critical parameters needed for the timing RPC wall are a time resolution , low crosstalk and an ef- ficiency above 95% for single hits [3] at the highest expected rates. Once the detector concept was validated in several tests performed in 2003 [5], [6], 2005 [7], [8] and 2007 [9] under realistic particle environments, and the overall stability of the FEE channels equipping a full sector was also validated in 2008, a cosmic ray commissioning was performed in 2009 before the final installation of the 6 RPC sectors. 0018-9499/$26.00 © 2010 IEEE