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 eight thousand 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 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 0.25μm CMOS technology, it dissipates 41mW. Each channel implements a low noise charge preamplifier with continuous reset of new concept, shaping amplifier with band-gap 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.