TARGET 5: a new multi-channel digitizer with triggering capabilities for gamma-ray atmospheric Cherenkov telescopes

TL;DR

TARGET 5 is an advanced ASIC for gamma-ray telescopes that enhances signal sampling, digitization, and triggering, improving performance metrics and enabling its use in the upcoming Cherenkov Telescope Array.

Contribution

It introduces TARGET 5, the first ASIC of its family used in an IACT prototype, with significant performance improvements over previous versions.

Findings

Sampling frequency tunable from <0.4 to >1 GSa/s

Charge resolution improves from 40% to <4%

Achieves stable trigger threshold of 20 mV

Abstract

TARGET~5 is a new application-specific integrated circuit (ASIC) of the TARGET family, designed for the readout of signals from photosensors in the cameras of imaging atmospheric Cherenkov telescopes (IACTs) for ground-based gamma-ray astronomy. TARGET~5 combines sampling and digitization on 16 signal channels with the formation of trigger signals based on the analog sum of groups of four channels. We describe the ASIC architecture and performance. TARGET~5 improves over the performance of the first-generation TARGET ASIC, achieving: tunable sampling frequency from $<0.4$~GSa/s to $>1$~GSa/s; a dynamic range on the data path of 1.2 V with effective dynamic range of 11~bits and DC noise of ${\sim}0.6$~mV; 3-dB bandwidth of 500 MHz; crosstalk between adjacent channels $<1.3\%$; charge resolution improving from 40\% to $<4\%$ between 3 photoelectrons (p.e.) and $>100$~p.e. (assuming 4 mV per p.e.); and minimum stable trigger threshold of 20 mV (5 p.e.) with trigger noise of 5 mV (1.2 p.e.), which is mostly limited by interference between trigger and sampling operations. TARGET~5 is the first ASIC of the TARGET family used in an IACT prototype, providing one development path for readout electronics in the forthcoming Cherenkov Telescope Array (CTA).