Front-end ASIC for a GEM based time projection chamber

A time projection chamber for experiments with the laser electron gamma source is being developed. It is composed of a can and a single-ended, dual-stage gas electron multiplier, with associated anode plane pixellated into about 8000 pads. The front-end electronics must provide energy, timing, and address information from those pads involved in measuring each track. For center of gravity determination this information must be sampled from the above-threshold pad and from the two adjacent ones. An efficient scheme for readout of the approximate to8000 front-end channels between each measurement cycle is also required. A 32-channel front-end application-specific integrated circuit has been developed to serve this detector. Fabricated in 0.25 mum CMOS technology, it dissipates 41 mW. Each channel implements a low noise charge preamplifier with continuous reset of new concept, shaping amplifier with bandgap referenced baseline stabilizer, single threshold discriminator, dual-phase peak detector, timing detector, and logic for neighbor enabling. The readout process is based on token passing and flag.