The XGIS instrument on-board THESEUS: the detection plane and on-board electronics
Fabio Fuschino, Riccardo Campana, Claudio Labanti, Lorenzo Amati, Enrico Virgilli, Luca Terenzi, Pierluigi Bellutti, Giuseppe Bertuccio, Giacomo Borghi, Francesco Ficorella, Massimo Gandola, Marco Grassi, Giovanni La Rosa, Paolo Lorenzi, Piero Malcovati, Filippo Mele, Piotr Orlea?ski, Antonino Picciotto, Alexandre Rachevski, Irina Rashevskaya, Andrea Santangelo, Paolo Sarra, Giuseppe Sottile, Christoph Tenzer, Andrea Vacchi, Zampa Gianluigi, Nicola Zampa, Nicola Zorzi, Paul hedderman, M. Winkler, Alessandro Gemelli, Ifran Kuvvetli, Søren Møller Pedersen, Denis Tcherniak, Lucas Christoffer Bune Jensen
TThe XGIS instrument on-board THESEUS:the detection plane and on-board electronics
F. Fuschino a,b , R. Campana a,b , C. Labanti a , L. Amati a , E. Virgilli a,b , L. Terenzi a , P. Bellutti c ,G. Bertuccio d , G. Borghi c , L. C. Bune Jensen g , F. Ficorella c , M. Gandola d , A. Gemelli e ,M. Grassi e , P. Hedderman f , I. Kuvvetli g , G. La Rosa h , P. Lorenzi i , P. Malcovati e , F. Mele d ,P. Orleanski l , M. Pedersen g , A. Picciotto c , A. Rachevski m , I. Rashevskaya m,n , A. Santangelo f ,P. Sarra i , G. Sottile h , D. Tcherniak g , C. Tenzer f , A. Vacchi o,n , M. Winkler l , G. Zampa n ,N. Zampa n , and N. Zorzi ca INAF/OAS, Via Gobetti 101, I-40129, Bologna, Italy b INFN-Sezione di Bologna, Viale Berti Pichat 6/2, I-40127 Bologna, Italy c Fondazione Bruno Kessler – FBK, Via Sommarive 18, I-38123 Trento, Italy d Department of Electronics, Information and Bioengineering (DEIB) of Politecnico di Milano,Como Campus, Via Anzani 42, 22100 Como, Italy e Department of Electrical, Computer, and Biomedical Engineering, University of Pavia, ViaFerrata 5, 27100, Pavia, Italy f Institut f¨ur Astronomie und Astrophysik, Abteilung Hochenergieastrophysik, Kepler Centerfor Astro and Particle Physics, Eberhard Karls Universit¨at T¨ubingen, Sand 1, 72076T¨ubingen, Germany g National Space Institute, Technical University of Denmark, Elektrovej building 327, Denmark h INAF, Istituto di Astrofisica Spaziale e Fisica cosmica di Palermo, via U. La Malfa 153,I-90146 Palermo, Italy i OHB-Italia, Via Gallarate, 150, I-20151 Milano, Italy l Space Research Centre, Polish Academy of Sciences, Bartycka 18A, 00-716 Warszawa, Poland m TIFPA-INFN, Via Sommarive 14, I-38123 Trento, Italy n INFN Italian National Institute for Nuclear Physics c/o Area di Ricerca, Padriciano 99,I-34127, Trieste, Italy o Department of Mathematics, Computer Science and Physics University of Udine, Via delleScienze 206, I-33100, Udine, Italy
ABSTRACT
The X and Gamma Imaging Spectrometer instrument on-board the THESEUS mission (selected by ESA in theframework of the Cosmic Vision M5 launch opportunity, currently in phase A) is based on a detection planecomposed of several thousands of single active elements. Each element comprises a 4.5 × ×
30 mm CsI(Tl)scintillator bar, optically coupled at both ends to Silicon Drift Detectors (SDDs). The SDDs acts both asphotodetectors for the scintillation light and as direct X-ray sensors. In this paper the design of the XGISdetection plane is reviewed, outlining the strategic choices in terms of modularity and redundancy of the system.Results on detector-electronics prototypes are also described. Moreover, the design and development of the low-noise front-end electronics is presented, emphasizing the innovative architectural design based on custom-designedApplication-Specific Integrated Circuits (ASICs).
Keywords:
THESEUS mission, Chipset, ORION, ASIC, Silicon Drift Detector, Scintillator crystals
Send correspondence to:Fabio Fuschino, E-mail: [email protected] a r X i v : . [ a s t r o - ph . I M ] F e b . INTRODUCTION The
Transient High-Energy Sky and Early Universe Surveyor (THESEUS
1, 2 ) is a space mission concept aimingat fully exploiting Gamma-Ray Bursts (GRBs) for investigating the early Universe and at providing a substantialadvancement of multi-messenger and time-domain astrophysics. THESEUS is currently in Phase A study bythe European Space Agency (ESA), as a candidate mission for the M5 slot for a possible launch in 2032. ThePhase A study will be completed in Spring 2021 with the final downselection to one candidate in Summer 2021.The THESEUS mission is planned to be launched in a low Earth orbit (LEO) with low inclination ( < ◦ ). Itsplanned nominal lifetime is 4 years, which ensures a sufficient number of high-redshift GRBs (according to theyearly rate of those type of events, which are among the main target of the mission) to be observed and studied.The THESEUS payload combines two high energy instruments with large a Field of View (FoV) working insynergy for transient events detection. The X-Gamma Imaging Spectrometer (XGIS) is a wide field deep skymonitor covering the 2 keV–10 MeV energy pass-band. The XGIS consists of two units, with imaging capabilityin the 2–150 keV band through the employ of a coded aperture mask. In this energy range the FoV is 77 ◦ × ◦ while above ∼
150 keV the instrument acts as a full sky spectrometer. The two XGIS units are pointed at ± ◦ offset with respect to the payload axis in a way that their FoV partially overlap. Extensive study of the expectedsources of background on the XGIS has been done and in particular of its effects on the instrument sensitivity .The THESEUS Soft X-ray Imager
5, 6 (SXI) comprises 2 detector units (DU). Its 0.3–5 keV energy pass bandpartially overlaps the XGIS energy range. Each DU is a wide field Lobster Eye telescope using the optical principlefirst described by Angel (1979) . The optics aperture is formed by an array of 8 × ×
40 mm and are mounted on a spherical frame with radius of curvature600 mm (2 times the focal length of 300 mm). The use of the Lobster Eye concept allows an unprecedentedcombination of large FoV (0.5 sr), source location accuracy ( < Infra-Red Telescope
8, 9 (IRT)which is composed by a primary mirror of 0.7 m of diameter and a secondary mirror of 0.23 m in a Cassegrainconfiguration. In imaging mode the IRT has a FoV of 15 (cid:48) × (cid:48) . Transient events that triggers in the FoV ofthe SXI and/or XGIS will be observed by IRT that will provide immediate identification systematically within afew minutes with sub-arcsecond position accuracy and spectroscopic redshift determination. An overview of theTHESEUS mission with its payload is given in Figure 1. The three instruments are coaxial and in particular,the SXI FoV is fully included in that of the XGIS.In the following Sections a detailed description of the XGIS will be given, focusing on the design of thedetection plane and on the related readout electronics. For each XGIS camera, a customized architecture forthe electronics is required, given the complexity and peculiarity of the detection plane, made with 12800 silicon-based detectors coupled in pairs to 6400 scintillator bars. The design of an Application Specific IntegratedCircuit (ASIC) chipset for the XGIS instrument, named ORION, is presented. Both ORION front-end (ORION-FE) and ORION back-end (ORION-BE) structures with their interaction are described. Simulation results of asingle-channel prototype, which is currently being experimentally characterized, are discussed.
2. XGIS: GENERAL OVERVIEW
The XGIS instrument is composed by two cameras which are tilted of ± ◦ in the two opposite directionswith respect to the satellite axis . To enable imaging capability for each XGIS Camera in the 2–150 keV energyrange, a coded aperture system placed 63 cm above the detection plane will be used. In order to provide effectivecoding of the sky in the full energy range, the coded mask opaque elements are 1 mm thick. In its imagingenergy range, the XGIS FoV fully overlaps that of the SXI. A collimator made of Al enclosing a W foil 0.25 mmthick limits the FoV of each XGIS Camera to 77 ◦ × ◦ . Under these assumptions the overall FoV of the XGISwill be 117 ◦ × ◦ . Each Camera is composed by a matrix of 5 × Super-Modules , while each Super-Module isin turn composed of 10
Modules . Finally, each Module consists of a matrix of 8 × <
30 keV) interact directly in theSDD, while for energies above 30 keV the indirect photon detection occurs with the photon interaction in theCsI(Tl) crystals. The resulting scintillation light, which is in the optical energy range, is collected by SDDs igure 1. An engineering drawings view of the THESEUS mission with the three on-board instruments. on both side of the crystal. Such configuration, allowing for a compact and efficient broadband single devicedetection unit, has been also called siswich (from Silicon-sandwich) in analogy with the phoswich detectionsystem successfully used in several experiments (e.g. PDS/BeppoSAX , HEXTE/RXTE , HE/HXMT ).The SDD size determines the spatial resolution of the detector. Furthermore, if the interaction occurs in thescintillator bar, by weighting the signals from the SDD at both ends (whose intensity is inversely proportionalto the distance between the interaction point and the SDD), the coordinate of the scintillation point along thebar can be estimated. Figure 2 illustrates the working principle of the siswich detection system, together withthe achievable detection efficiency.In the XGIS configuration, each CsI(Tl) bar has dimensions 5 × ×
30 mm , the longer dimension along thethe XGIS Camera axis. A custom electronic read-out will distinguish the two kind of signals, depending on theinteraction that can occur directly on the topmost SDD (the one facing the sky) or on both SDDs, meaning thatthe radiation interacted in the CsI(Tl) bar. In particular, electron-hole pair creation from X-ray interaction inSilicon generates a fast signal (about 100 ns rise time). On the other hand, due to the fluorescent light componentand crystal characteristics, the scintillation light collection is emitted and collected in a much longer timescale(typically 1–2 µ s).The segmented structure leading progressively from a single SDD+CsI(Tl)+SDD pixel to a camera (Figure 2)and to the XGIS full system is also explained with the diagram shown in Figure 3 in which are also reportedthe sub-systems correlated to each structure of increasing complexity. In particular, the highlighted blocks arethose directly connected both to the modularity of the instrument and to its associated electronics. These twotopics are the subjects of this paper. In the following Sections we will describe the Module ORION ASIC, theSuper-Module back-end electronics (BEE) and the Camera BEE, respectively. Finally, a general description ofthe XGIS system will be reported with particular highlight to the the power distribution, to the Data HandlingUnit (DHU) and to the total power consumption of each XGIS camera. igure 2. Top left: the working principle of a siswich detection system. Two SDD are placed at both ends of a CsI(Tl).The low energy radiation (below ∼
30 keV) interacts in the SDD. Photons with energy above a certain threshold crossthe SDD and interact in the scintillator bar. The light output is collected at both SDD coupled with the CsI(Tl) bar.
Bottom left: efficency vs. photon energy for the direct detection in the SDD (black curve) and through light conversionin the CsI(Tl) (blue curve).
Right: design of one XGIS camera on board THESEUS.Figure 3. Block diagram showing the XGIS systems and subsystems. In the present paper we focus on the modularityof the XGIS (cyan blocks) with increasing complexity from left to right and on the electronics (yellow blocks).
3. XGIS MODULE SILICON SENSORS: SDD
Due to the the peculiarity of the detector architecture of the combined detection of X and Gamma radiation inthe THESEUS XGIS instrument, a fully custom SDD matrix design is needed. The SDD development activityis a natural progress of the developments carried out within the ReDSoX research program ∗ financed by INFNand co-financed jointly by FBK for the part related to the SDD technology.In particular, the XGIS application provides the optical coupling of two SDD sensors to the opposite faces of ∗ http://redsox.iasfbo.inaf.it scintillator bar to detect the light generated by the interaction of gamma radiation within the crystal. In thisconfiguration, the SDD sensor is also capable of detecting the X radiation impinging on the face not coupled tothe crystal, facing the sky. This solution is also suitable to the realization of a detector with imaging capabilityby packing together a certain number of scintillator bars read out by monolithic SDD sensor matrices. In theReDSoX context, some SDD sensor prototypes dedicated to this application have been designed, implementedand characterized. Already in the early stages of prototype development, the size of the scintillator bar sectionwas originally chosen as 5 mm × × ∼ Figure 4. XGIS SDD array with 8 × Left : the n -side, with collecting anodes. Right : the p -side thatwill be optically coupled to scintillators The n -side of the detector will be directly exposed to radiation. The sensitive area for X-rays detection, whichin principle is the geometrical area 5 × of each array element, is instead reduced due to a partial obstructionmade by the assembly PCB. At the end, the final sensitive area will be defined by the definitive version of theassembly PCB. The p -side of the detector will be optically coupled to the scintillators. To guarantee an adequateoptical separation between adjacent elements, a 0.5 mm wide Al track is deposited between the SDD elements,thus reducing the sensitive area for the scintillation light to 4.5 × .The depletion voltage of each SDD (VDEPL), is strongly linked to the doping concentration of the substratesand then for a large area detector the doping uniformity at wafer level is crucial. For devices manufactured inthe same production run with the same substrate batch VDEPL uniformity level well fit the requirements forthe production of the XGIS sensor for THESEUS. However for XGIS-Camera we foresee to select SDD withuniform VDEPL for the same Super-Module (assembly with 10 Modules mechanically and logically connected),regulating the VDEPL at Super-Module level via TLC. A first production of such devices, to both check theprocess flow and the device layout, has been carried out in FBK during the first part of 2019 and concluded inJune 2020. Such batch results in a multi-project wafer assembly. Preliminary measurements were performed inFBK to acquire the IV-total curve, with the aim to estimate the leakage current density for each SDD array,as a kind of production quality check. From such measurements, SDD arrays results in very low-level leakagecurrent density, estimated to be <
200 pA/cm measured at +24 ◦ C, then considered very promising for further able 1. Main parameters of the SDD array
Array size 42.4 × Si thickness 450 µ m × Single SDD active area for scintillator (p side) 4.5 × Metal grid between single SDD (p side) 0.5 mm wideTypical polarization voltage (1 connection for the whole array) –100 ÷ –150 VTypical return voltage (1 connection for each SDD) –12 ÷ –20 VSingle SDD capacitance 50 fF (typical)Dark current (typical at T = 20 ◦ ) 50 pA (typical)Optical spectral response 350 – 1000 nm (typical)QE >
4. XGIS MODULE READOUT ASIC: ORION
The electrical signals from the SDD anodes are collected and processed by the ORION chipset, a constellationof ASICs composed by the ORION-FEs, for the charge readout and the initial signal shaping placed in closeproximity of the SDDs, and the ORION-BEs for the complete signal processing and digitization. The simplifiedschematic of the ASIC readout architecture is shown in Figure 5. A similar structure is adopted in the HERMES(
High Energy Rapid Modular Ensemble of Satellites ) nano-satellites mission
18, 19 in which the ASICs of the LYRAfamily (LYRA-FE and LYRA-BE) are employed.The ORION chipset is responsible for both the analog readout of the SDD charge and for the digitization anddata communication of the event information to the module electronics. For each detected event, the ORIONASIC is able to provide the energy of the event, the type of the event (i.e. X or γ ) the position of the event(i.e. pixel coordinates) and the timing of the event with respect to an external clock. The ORION chipset iscomposed by a total of 12800 analog ORION-FE that send a pre-shaped signal to 800 mixed-signal back-endmulti-channel chips (8-channels ORION-BE) for dedicated signal processing and digitization. Figure 5. Structure of the electronics for collecting and processing the SDD signals based on the ORION-FE andORION-BE ASICs.
Due to the peculiar architecture of the ASIC, each single channel ORION-FE is physically placed closeto the SDD anode, in order to keep the stray capacitance at the preamplifier input as low as possible. TheRION-FE single channel collects the SDD generated charge and performs pre-amplification. The ORION-BE,that is physically placed a few cm away on the bottom of the module, receives the signals from 8 × Figure 6. Structure of the electronics for collecting and processing the SDD signals based on the ORION-FE andORION-BE ASICs. Figure 7. The ASIC architecture related to a pixel.
Figure 7 shows the general ASIC architecture for a single pixel, which, as discussed previously, is composed bytwo SDD optically coupled with a CsI(Tl) bar at both ends. The rationale for this architecture is the following: • If an X-ray (2–30 keV) is detected only in the top SDD (hereafter called
X-mode event ):1. The preamplifier output signal is fast (hundreds of ns).2. As the X-ray detection is (almost) point-like in the SDD, the arriving time of the signal at the SDDanodes is delayed up to 1 µ s with respect to the event occurrence, due to the drift time of the electroncloud within the SDD. The time marking of the event is then affected by the uncertainly due both tothe jitter of the trigger and to the unknown position of the interaction in the SDD (Figure 8).. The best signal/noise ratio is achieved with a short shaping time (1 µ s typical).4. The discrimination between X-ray and γ -ray is done only using the top SDD signal (see below). • If a γ -ray ( >
20 keV) is detected simultaneously in top and bottom SDDs (hereafter called γ or S-modeevent ):1. The preamplifier output signals is slow (of the order of few µ s), in agreement with the typical scintil-lation decay time.2. The scintillation light is spread across the whole SDD, therefore both scintillation time and maximumdrift time of the charge should be taken into account to avoid ballistic deficit.3. The best signal/noise ratio is achieved with shaping time of the order of 3 µ s (typical).4. The amplitude discrimination is achieved operating on the sum of top and bottom SDD signals. • Mixed X-ray/ γ -ray events in time coincidence can occur with quite low probability (few % even at thehighest photon energies). Figure 8. The time marking of the X and γ -events. Left : an X event is detected only in the top SDD but the timetag is affected by both the trigger jitter combined with the uncertainty due to the charge drift time due to the unknowninteraction position within the SDD cell.
Right : the time tag of a γ -event depends on the trigger jitter combined with alonger signal collection due to the fluorescence light component. The ORION-FE is a fully-analog ASIC conceived to provide the first amplification of the charge signal comingfrom the SDD, keeping a low area occupation ( ∼ ) in order to allow a close connection to each anode,without compromising the detection area. The ORION-FE is mainly divided in three stages: a Charge SensitiveAmplifier (CSA) with a dynamic range of 32 fC, followed by a pole-zero compensation stage and a currentconveyor, which additionally introduces a first CR shaping with 1 µ s time constant. To avoid spurious injectionthe CSA is operated in continuous reset mode, and the output of the ORION-FE is delivered as a current signalgenerated by the current conveyor itself . Each ORION-FE has a power consumption of 290 µ W at T = − ◦ C,which also includes the contribution from the internal biasing module and of the Electrostatic Discharge (ESD)protection module.
The signals generated by the top and bottom ORION-FE of each pixel are transmitted as current signals on ∼ γ -ray event, while the signal coming from the top SDDcannot be a priori identified as an X or γ -ray event, and the output of the top current receiver is sent to bothX-/ γ processing channels, which operate with peaking times of 1 µ s and 3 µ s, respectively. The stretched outputvoltage is then digitized by a second-order 12 bit ENOB incremental A/D converter. After the conversion, thepixel logic is able to discriminate the type of detected event, with the respective timestamp, and eventuallyforward the information to the on-board module electronics. Each read-out BE channel is thus made up bythree parallel paths, each one including also an independent ADC. Even if the BE discriminators deliver X and related triggers on a given event, due to the nature of the instrument, this information is fundamental butnot sufficient to determine the type of event. For this reason the ADC outputs as well as the triggers from theBE are processed by a dedicated logic which has the double aim of extracting the type of event, assigning thetimestamp and creating the digital output frame. This frame will include information on the event time, thetype of event, its address, the discriminators triggered during the event and, in probe mode, further informationuseful for detailed characterization of the ASIC, such as, for instance, the signals on the internal ADC buses. Inprobe mode through a multiplexer and a buffer also all the analog outputs of the BE channels and their triggersare available for external measurement. Finally, in the multi-channel ASIC several channels may trigger togetherfor a common event. For this reason, the embedded logic waits a programmable time, named RTP (Rise-TimeProtection), before sampling all the BE signals (analog and triggers), starting the data conversion and finallybuilding the output frame. When the frame is ready, a Look at Me (LaM) signal is given. The ORION ASICembeds 1-kbit memory bank for SDD read-out analog channel configuration, for internal logic settings and fortemporary output frame storage. The configuration and the output frames can be loaded/read-out either througha shift register or an SPI interface, based on a 4-wire bus plus reset. The ORION-BE has a power consumptionof 980 µ W per pixel (including both X/ γ channels) at T = − ◦ C. The ORION chipset has been simulated to have an Equivalent Noise Charge (ENC) (with a detector capacitanceof 50 fF and a leakage current of 0.7 pA) of about 12.5 e − r.m.s. at 1 µ s of peaking time on the X channel and32.9 e − r.m.s. at 3 µ s on the γ channel. Despite a very wide input dynamic range on the γ channel (from 400e − to 180 000 e − ) the expected linearity error is below ± ± ad hoc for the ORION ASIC, featuring 11.9 bits including both noise and distortion effects. Figure 9. Simulated noise for different input leakage currents, corresponding to the expected Beginning-Of-Life (0.7 pA)and End-Of-Life (700 pA) performance of the detector.
5. SUPER-MODULE AND CAMERA BACKEND ELECTRONICS
A XGIS Super-Module is a logical and hardware subset of the detector assembly and consists of 10 Modulesjoined with a Super-Module Back End Electronics board (SM-BEE). The segmentation of the XGIS camera in igure 10. A detailed layout view of the ORION-FE (left) to be placed in close proximity of the SDDs and of the singlechannel prototype of the ORION-BE (right). In the top-left corner of the ORION-BE, the analog BE module, with thetwo small-pad inputs, is visible. The analog-BE as well as the ADCs are realized on a modular layout structure, for easeof implementation in multi-channel architectures.Figure 11. ORION ADC elementary module output spectrum applying a 1 kHz sinusoidal signal at full scale
Super-Modules allows to mitigate the effects of a potential system failure that, in case of occurrence at Super-Module level, would consist in a reduction of only 10% of the sensitive area. The modularity at the ASIC levelensures that in case of failure of an ASIC only 8 pixels are unusable. By exploiting the same concept, for eachdetected event, only 8 pixels get “frozen” leading to a dead time interval (since the corresponding ASIC is busy).On the contrary, it allows to perform parallel acquisition of contemporary events falling in non-adjacent pixels.The segmentation in Super-Modules also ensure a remarkable reduction of the connections between ORION-BE ASIC and FPGA (5 lines), of the total FPGAs used in a XGIS Camera (10 FPGAs) and of components(ADCs+Logic embedded into the ASICs). For each XGIS-Camera is also planned to install selected SDD withuniform depletion voltage (VDEPL) in the same Super-Module, with the possibility of regulating the VDEPLat Super-Module level via telecommands. The possibility, for large area detectors, of a fine tuning of VDEPL iscrucial. In Figure 12 are shown a general view as well as an exploded view of a single Module together with thefull detection plane in which is highlighted its partition in 10 Super-Modules.The SM-BEE provides the power supply to 10 Modules, commands the Modules, collects the data (events/HKs)from the Modules and interfaces all the functions (commands, HKs, Alarms, Data) with the XGIS Camera BackEnd Electronics (C-BEE). The architecture of the SM-BEE will be built around one FPGA that will control 80Orion-BE ASICs with a logic as depicted in Figure 13 whose main characteristics are: • for the I/F with each single ORION-BE ASIC there are only 5 logic lines between the FPGA (where 3 ofthem are in common); igure 12. Left : A Module of the XGIS in which are visible the different parts that compose the detector pixels and thePCBs.
Right : an XGIS Super-Module (highlighted in red) which is made with 10 Modules. One entire XGIS camera,which is also visible in figure, is made with 10 Super-Modules. • the FPGA of the SM-BEE manages 160+3 = 163 logic lines in total (I/O pins); • the I/F with the C-BEE will be buffered with a memory of proper size; Figure 13. Logic concept of the Super-Module Electronics. One FPGA manages 80 ORION-BE and 10 SM-BEE areconnected to the Backend Electronics of the Camera (C-BEE).
The XGIS Camera is managed through a Camera Back End Electronics board (C-BEE) which is organisedin two logical sections, in cold redundancy, each connected to the DHU main and redundant section respectively,and simultaneously connected with the 10 SuperModules. The main functions of the C-BEE are of providingpower supply distribution and management of all Super-Modules and of power supply interface with the XSU.Other functions of the C-BEE are: Data I/F with all Super-Modules, Data buffering and I/F with XGIS-DHU, telecommands I/F with XGIS-DHU, telecommands implementation and verification, HK managementand transmission to XGIS-DHU and Alert management. The logical connection between SuperModules andXGIS-DHU through C-BEE is shown in Figure 14.
6. XGIS ELECTRICAL ARCHITECTURE
Beside the 2 XGIS-Cameras, two 2 XGIS Supply Units (XSUs) and a DHU compose the XGIS instrument. TheXSUs will be contained in two boxes each one supplying one XGIS-Camera. The electrical architecture of the igure 14. Logical connection between Super-Modules and XGIS-DHU through C-BEEs
XGIS is shown schematically in Figure 15 in which functional blocks of XGIS instrument and their interfaceswith the THESEUS spacecraft platform are shown. Central element in the XGIS operation and data acquisitionchain is the DHU that serves as telecommand/telemetry and power interface between the Spacecraft ServiceModule (SVM) and the XGIS-Cameras. The on-board burst trigger capability is implemented as a part of theDHU, which is directly interfaced with the on-board data handling (OBDH) system. The electrical interfaceis assumed to be SpaceWire. Each C-BEE is connected to the DHU for control, data, and health monitoring.The bus power is routed through the XSU power distribution unit providing ON/OFF switching and protectioncapability, with an overall power consumption of about 210 W (included margins) for each camera.
Figure 15. Functional block diagram of the XGIS system, consisting of 2 identical cameras. Each camera is made of 100Modules organized in 10 Super-Modules), 2 power distribution boxes (XSU) and a Data Handling Unit (DHU) (in coldredundancy).
7. SUMMARY AND PROSPECTS
In this paper we have shown the main features of the XGIS on board THESEUS. In particular we have describedthe ASIC ORION-FE and ORION-BE which has been developed specifically for the THESEUS mission concept.he concept of having the electronic chain split in two ASICs as in the LYRA FE and BE case has been testedwith success in the context of the HERMES nano-satellite mission. First prototypes of the ORION-FE andORION-BE ASICs have been assembled and are currently in testing and characterization.
ACKNOWLEDGMENTS
The authors wish to thank the European Space Agency for its support through the M5/NPMC Programme andthe Italian Space Agency and the National Institute of Astrophysics for their support through the ASI-INAFAgreement n. 2018-29-HH.0., the OHB Italia/INAF-OASBo Agreement n.2331/2020/01.
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