Speaker
Description
Brookhaven National Laboratory is developing CHARMS, a family of cryogenic front-end ASICs in 65-nm CMOS for low-noise readout of charge and light signals in noble-liquid detectors. Building on experience with the LArASIC chip, developed for liquid-argon time projection chambers and being deployed for the DUNE Phase-I far detectors, CHARMS moves to a more advanced CMOS technology and incorporates digitally assisted analog functions to provide greater flexibility, configurability, and robustness for future detector systems. Target applications include the DUNE Phase-II far detectors and the noble-liquid electromagnetic calorimeter proposed for the ALLEGRO detector in FCC-ee.
The first prototype, CHARMS250V1, is a single-channel ASIC with programmable charge gain from approximately 4 to 25 mV/fC and peaking time from 250 ns to 2 µs. The chip has been fabricated and characterized at both room temperature and liquid-nitrogen temperature, demonstrating excellent low-noise cryogenic performance. This contribution will present the CHARMS250V1 architecture and circuit design, together with results from its electrical and cryogenic characterization.
The liquid-argon calorimeter in the ALLEGRO detector introduces the additional challenge of resolving minimum-ionizing-particle signals of approximately 4 fC while accommodating input charges approaching 10 pC with 12-bit resolution. To address this wide dynamic range, a second prototype, CHARMS250V2, is being developed to extend the full-scale input charge range to 10 pC while preserving the low-noise performance demonstrated with CHARMS250V1. Two front-end architectures are currently being investigated to achieve this goal. The first approach (CHARMS250V2A) employs dual parallel gain paths, with a high-gain path optimized for low-noise operation and a low-gain path enabling large dynamic range. The second approach (CHARMS250V2B) utilizes dynamic feedback capacitance switching in the charge amplifier, providing low-noise performance for small input charges while achieving large dynamic range with acceptable noise for higher input signals. The design and expected performance of CHARMS250V2A and CHARMS250V2B will also be presented.