The Design and Performance Characteristics of the NRL4 ASIC Developed for the COSI Small Explorer Gamma-ray Satellite

TL;DR

This paper presents the NRL4 ASIC, a low-power, low-noise 32-channel front-end electronics chip designed for high-resolution gamma-ray detection in space and balloon missions, demonstrating promising performance with germanium detectors.

Contribution

The paper introduces the NRL4 ASIC with advanced features tailored for gamma-ray spectroscopy, highlighting its integration with germanium detectors and its low-power, high-resolution capabilities.

Findings

Achieved 3 keV FWHM energy resolution at 59.54 keV

Demonstrated low-noise, configurable gain channels

Validated suitability for space-based gamma-ray missions

Abstract

Next-generation gamma-ray observatories aim to enable precision measurements in high-energy astrophysics using advanced semiconductor detector technologies. Meeting the scientific requirements of modern instruments demands detector systems that provide high spatial and spectral resolution across large detection areas, with strict limits on power consumption and mass. These needs drive innovation in front-end electronics and mixed-signal processing to support compact detector electrode geometries. Application-specific integrated circuits (ASICs) are essential in front-end readout electronics, enabling high-channel-density and low-power systems, while maintaining low-noise performance suitable for space-based instruments and balloon-borne payloads. The NRL4 (Naval Research Laboratory 4) is a recently developed 32-channel front-end ASIC featuring low-power, low-noise channels consisting of charge-sensitive preamplifiers, 4 configurable gain settings, dual configurable shapers for optimized timing and energy resolution, trimmable per-channel discrimination, time-to-analog conversion, and peak-detect output. The NRL4 has been integrated with a high-purity germanium (HPGe) dual-sided strip detector with a 1.16 mm strip pitch. Energy resolution of 3 keV full width at half maximum (FWHM) at 59.54 keV was achieved with a gain of 18.4 mV/fC and a slow shaper peaking time of 2 {\mu}s. Preliminary results from ongoing research demonstrate the suitability of the NRL4 for high-resolution, low-power gamma-ray spectroscopy for ground and space-based missions.