A Novel Front-End ASIC for the Beam Particle Monitor of the CSR External-Target Experiment

A beam particle monitor, which is designed to locate the position of each beam particle, is a part of the cooler-storage-ring external-target experiment at the heavy-ion research facility in Lanzhou of China. A novel front-end ASIC integrating charge sensors and readout circuitry on a single silicon chip is used to sense and read out the charge for the beam particle monitor. The ASIC operates within a gaseous ionization detector to detect drifting charges. The area of the ASIC is about 3 mm × 19 mm. It features 180 channels with a pitch of 100 μm and an event-driven zero-suppression readout scheme. Each channel is composed of a charge collection electrode, a charge-sensitive amplifier, a discriminator, an amplitude measurement with the time-over-threshold method, and an arrival-time measurement with the time-to-digital converter method. The charge collection electrode is an exposed top-most metal with a size of 1 mm × 89 μm. Three selectable gain modes are designed in the charge-sensitive amplifier, in order to increase the input dynamic range. The decay time of the charge-sensitive amplifier and the threshold of the discriminator in each channel can be adjusted independently by local digital-to-analog converters, hence reducing the inconsistency between channels. Detailed tests have been performed. The equivalent noise charge ranges from 344 e–. to 378 e–. and the fixed pattern noise is approximately 97 e–. after the threshold adjustment. The minimum shaping time is about 500 ns. The arrival time resolution is from 9 to 13 ns depending on the drifting distance. The variations of the noise and the threshold during long-term running are less than ±1.5% and ±0.3%, respectively. The total ionization dose test, laser beam and heavy-ion beam tests have also been carried out.