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The power supply system for the front-end electronics of the HADES resistive plate chamber (RPC) detector, installed at GSI (Darmstadt, Germany), is described. The system has a distributed architecture that includes custom low-voltage boards using isolated dc--dc switching converters. These converters are compact and operate at high efficiency. The converters are fitted with input and output electromagnetic interference filters, resuiting in very low output noise. Operational tests of the RPC detector demonstrate that the performance of the detector when powered by this system is comparable to that achieved when powered by laboratory bench supplies, proving its suitability for large-scale applications requiring time resolutions better than 100 ps. Index Terms--Distributed power system, HADES, low-noise power supplies, low-voltage system, power-supply system for time-of-flight, switching converters for physics experiments.

HADES is a running spectrometer installed at GSI, Germany. PANDA and CBM are planned detector systems for the new FAIR facility at GSI. For these detectors, a general-purpose trigger and readout board with on-board DAQ functionality was developed. The original motivation for this project was the implementation of a 128-channel time to digital converter (TDC) with a time resolution of [sigma] = 40 ps based on the HPTDC chip from CERN into a fully fledged data acquisition system. The application of the board is detector independent, includes a 2 Gbit/s optical link and has the option to employ the TDC chips and/or to integrate versatile add-on boards through 16 Gbit/s connectors. The latter one may interface to the front end electronics of other types of detectors. A large FPGA (Xilinx Virtex 4 LX40) and a TigerSharc DSP can be used as on-board resources for trigger and on-line analysis algorithms. Data transfer to mass storage and slow control is done via an ETRAX processor running Linux and a 100 Mbit/s Ethernet interface. Index Terms--Data acquisition, modular electronics, time measurement, triggering.

The multi-level trigger system of the HADES detector is intended to select dilepton events in heavy ion reactions and to reduce minimum bias event rates by a factor of 10000. After a first level trigger based on the charged particle multiplicity the second level is the essential dilepton trigger which identifies electron signatures in several detector components and correlates them to dileptons. The third level trigger verifies these dilepton candidates using additional tracking information. Programmable logic devices, FPGAs and CPLDs, as well as DSPs are widely used to gain flexibility and provide common solutions. The trigger concept and fully functional versions of the readout boards and the second level trigger are presented.