# A Survey of Analog-to-Digital Converters for Operation under Radiation Environments
## 1 Introduction  
Several high reliability applications such as HEP (high energy physics), avionics, defense and space demand ADCs operating in harsh radiation and extreme temperature environments [1; 2]. The design, manufacture and test of these ADCs require additional considerations and steps that, added to their low volume market, increase their price compared to COTS (commercial off-the-shelf ADCs). Different fields of knowledge--solid-state and nuclear physics, manufacturing technologies, radiation hardening and mixed-signal design techniques, test methodologies, industry standards, etc.--have to be combined to achieve a successful design. The lack of ADCs meeting at the same time demanding electrical performance and radiation hardness specifications allows the use of COTS for high reliability applications. Furthermore, COTS could also be convenient in low radiation environments or in applications allowing replacement of damaged parts. Therefore, many COTS have been characterized to predict their behavior under radiation [3; 4; 5]. In fact, using COTS could economize development time and cost; however, radiation characterization cannot be skipped and additional countermeasures at system level--shielding, redundancy, watch-dogs, etc.--could be required to avoid unacceptable system malfunctioning. In addition, different manufacturing lots could perform differently during TID (total ionizing dose) screening, making hard to predict the final cost of the qualification campaign of COTS. In any case, inserting advanced commercial electronics operating in radiation environments has become an industrial trend that aims to benefit from cutting-edge IC (integrated circuit) solutions togetherwith ad-hoc radiation hardening techniques at system level. Our revision work takes COTS into consideration and analyses this subset also separately. Technology scaling has allowed faster applications integrating more functionalities in a single chip; collaterally, sensitivity to radiation has also varied [6; 7]. In fact, atmospheric radiation can affect deep-submicron CMOS (complementary metal-oxide semiconductor) ICs not only in-flight but also on land [8; 9]. Fortunately, some modern 'More Moore' [10] process options--SOI-FinFET (silicon on insulator fin-shaped field effect transistor), UTBB-FDSOI (ultra-thin body and buried oxide combined with fully-depleted silicon on insulator), etc.--and materials--high-\(\kappa\) dielectrics, germanium or silicon-germanium p-channels, etc.--show enhanced resilience to radiation [11; 12; 13]. Recurrent ADCs in space applications are usually implemented with mature technologies due to their in-flight heritage and the wide voltage ranges handled by the integrated analog front-end. Nevertheless, recent space market trends like fleets of compact-size satellites based on SoC (system on-chip) ICs require new radenv-ADC IP-cores (intellectual property) with reduced area and power consumption that can only be achieved with modern technologies. New radenv-ADC developments can benefit from the analyses presented in our work, since it collects the key references to overcome. Several FOMs (figures of merit) are defined in the literature to evaluate the efficiency of an ADC; many of them are collected in [14]. Unfortunately, parameters used to evaluate radiation performance of radenv-ADCs are not considered in these FOMs. Moreover, radiation-hardened ADCs require additional power to accomplish their radiation requirements, making unfair their comparison with unhardened devices. In Section 2.3, we propose new figures of merit to evaluate the efficiency of radenv-ADCs that consider not only their electrical performance but also their radiation characterization. In this work, we extract patterns on conversion resolution, characteristic frequencies, radiation performance, power efficiency, architectures and manufacturing processes of radenv-ADCs.