ORION, a Multichip Readout Electronics for Satellite Wide Energy Range X-/γ-Ray Imaging Spectroscopy: Design and Characterization of the Analog Section

The ORION chipset, a full-custom multichip readout and processing electronics for the X-
$\gamma $
-ray imaging spectrometer (XGIS) on-board the transient high-energy sky and early universe surveyor (THESEUS) space mission, is presented. The XGIS detection plane is arranged in a matrix of 10
$\times $
10 detection modules, each one composed of 64 CsI(Tl) scintillation bars (4.5 mm
$\times $
4.5 mm
$\times $
30 mm) optically coupled at the top and bottom ends to two 8
$\times $
8 monolithic silicon drift detector (SDD) matrices. The top SDD, exposed to the X-ray entrance window, performs the double function of low-energy X-ray detection as well as scintillator’s readout, together with the bottom SDD, providing detection and spectroscopic energy range from 2 keV up to 20 MeV. The need to achieve a high-energy resolution, as well as a high sensitive area on the detection plane, led to the development of a chipset organized to have a minimum-area analog readout chip placed in close proximity of the SDD (ORION-FE) and a mixed-signal back-end (ORION-BE) placed a few centimeters further on the back-end board for the additional signal processing and digitization. The multichip readout electronics integrates two dedicated analog processors for low-energy photons up to 30 keV (X-processor) and high-energy photons up to 5 MeV (
$\gamma $
-processor), allowing a spectroscopy-grade resolution in the 4 decades energy band (2 keV–20 MeV) of the XGIS, with a simulated power consumption of 1.55 mW/pixel. The ORION prototype was bonded to two ~25 mm
²
SDDs, and extensively characterized in terms of pulse shaping, pulse discrimination, and stretching functionality, as well as linearity, dynamic range, and spectroscopic resolution. An optimum equivalent noise charge (ENC) at −20 °C of 24.3 el. r.m.s. on the X-channel [212 eV full-width at half-maximum (FWHM) on Si], and 39.6 el. r.m.s. on the
$\gamma $
-channel [3.7 keV FWHM on CsI(Tl)] has been recorded.