IBEX: Versatile Readout ASIC With Spectral Imaging Capability and High Count Rate Capability

IBEX is a novel mixed-mode CMOS application-specific integrated circuit (ASIC), developed at DECTRIS Ltd., dedicated to the readout of hybrid photon counting semiconductor pixel detectors. The chip has been strictly designed in a radiation tolerant enclosed transistor layout and is fabricated in a 110-nm CMOS technology with eight metal layers. It consists of a 256 x 256 matrix of 75 x 75 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> pixels, which results in an overall chip size of 19.27 x 19.76 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> with periphery, supply, and I/O pads included. A so-called merging mode allows for an increased pixel size of 150 x 150 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The pixel readout electronics supports electrons and holes collection, and consists of a charge sensitive preamplifier with programmable gain, a shaper, and two comparators that allow for two independent energy thresholds. In the merging mode, the number of energy thresholds is increased up to four. In order to minimize the pixelto-pixel energy threshold variation, each pixel comparator can be adjusted with a 6-bit trim digital-to-analog converter. The ASIC can operate in a continuous readout mode with two independent 16-bit counters or in a high counting range mode with a single 32bit counter per energy threshold level. The chip features counter overflow handling and an instant retrigger technology with an adjustable retrigger time for a significantly improved high-rate counting performance. The ASIC offers a selectable external data bus width of 4, 8, or 16-bit. The count rate limit of the readout chip dc-coupled with a silicon sensor lies at around 10 Mcts/s/pix. The measurements show an electronic pixel noise of 89 e <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> rms and the detectable photon energy range between 3 and 160 keV.