Front-End ASIC for the STROBE-X HEMA and WFM Detectors: Concept and Design

TL;DR

This paper introduces the NSX front-end ASIC designed for the STROBE-X mission's X-ray detectors, featuring low noise, event-triggered readout, and advanced communication capabilities for efficient charge signal processing.

Contribution

The paper presents a novel ASIC design with low noise, event-triggered measurement, and inter-chip communication features tailored for space-based X-ray detector arrays.

Findings

Achieves a charge resolution of about 2.8 e- (unloaded) and 10.7 e- (connected to SDD)

Provides a FWHM of approximately 145 eV at 6 keV energy range

Power consumption per channel is around 590-670 μW

Abstract

This paper presents the NSX front-end ASIC, being developed to read charge signals from the HEMA and WFM X-ray detectors for the STROBE-X mission. The ASIC reads out signals from up to 64 anodes of linear Silicon Drift Detectors (SDDs). When unloaded, the ASIC channel has a charge resolution, expressed in Equivalent Noise Charge (ENC) of about 2.8 e-. Once connected to the SDD anode we anticipate, for the 80 keV energy range, a ENC of about 10.7 e- at a leakage current of 2 pA, which corresponds to a FWHM of about 145 eV at 6 keV once the Fano-limited statistics from charge generation in Si is included. The acquisition is event-triggered and, for events exceeding the threshold, the ASIC measures the peak amplitude and stores it in an analog memory for subsequent readout. The ASIC can also force the measurement of the sub-threshold channels neighboring the triggered channel, including the ones that belong to neighbor chips by using bi-directional differential inter-chip communication. Alternatively, the ASIC can measure the amplitudes of all channels at the time of the first detected peak. Additional features include a high-resolution option, channel power down and skip function, a low-noise pulse generator, a temperature sensor, and the monitoring of the channel analog output and trimmed threshold. The power consumption of the individual channel is ~590 $\mu$W and, when including all shared circuits, it averages to ~670 $\mu$W / channel.