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Description
The CoRDIA project aims to develop an X-ray imager capable of continuous operation in excess of 100 kframe/s. The goal is to provide a suitable instrument for Photon Science experiments at diffraction-limited Synchrotron Rings and Free Electron Lasers considering Continuous Wave operation.
Individual circuit blocks (adaptive-gain amplifier, analog-to-digital converter) were produced using a 65nm process and characterized, confirming expected performances.
A prototype has been designed, assembling said blocks in a pipelined, modular structure that can be replicated in a 2D pixel array.
Manufacturing is expected in spring 2023. Design architecture, expected performances and first test results will be reported.
Summary (500 words)
The upgrade of Synchrotron Rings toward the diffraction limit demands an upgrade of X-ray imagers to faster, continuous operation. Such devices are also needed to exploit the potential of high repetition-rate Free Electron Lasers considering Continuous Wave operation.
The CoRDIA (Continuous Readout Digitising Imager Array) detector aims at providing a hybrid detector capable of photon discrimination at 12 keV (also compatible with high-Z sensors for higher energies), a substantial full well, a compact pixel size (~100um), and continuous readout capability at a frame rate of ~150 kHz.
A first prototype including circuit blocks (analog front-end, analog-to-digital converter) has been manufactured in TSMC65nm technology, confirming expected performances [1].
A second prototype has now been designed, with the goal of signal-processing images in a pipeline fashion (so that one image is acquired at the same time the former one is digitized and streamed out), while at the same time arraying the circuits in a modular “superpixel” structure can be replicated in a 2D matrix in the readout ASIC.
The design (Figure) integrates the ADCs and the silicon area reserved for transmission drivers within the pixel array area (along with the analog front-end circuits), rather than relegating them to a periphery outside of the array (that would result in blind regions in a multi-chip assembly). The bump-bond pads interfacing to the sensor are redistributed to a uniform 2D array to facilitate bonding.
The circuits in the analog Front-End are designed using a standard-cell template for easiness of reuse, Place&Routing, and compatibility with existing digital designs, while trying to implement some RD53 recommendations to mitigate the impact of ionizing radiation. The Front-End includes an adaptive-gain circuit to extend the dynamic range, inspired by the AGIPD detector [2].
The Front-End to ADC interface consists in two sets of Sample/Hold cells that allow parallel charge integration of an image (at 150kHz), while charge integrated during the former image is sequentially passed to a Successive Approximation Register (11bit) digitizer (at 2.5MS/s), serving the 16 pixels included in the “superpixel” modular structure. Both circuits have proven to work within expected performances as insulated units; the purpose of the second CoRDIA prototype is to verify their operation as a circuital chain.
The superpixels are arranged in a mirrored double-column fashion around the common silicon area reserved for the output driver. Rather than develop a new high-speed driver, we decided to adopt the PCS-GWT solution developed by NIKEF for Timepix4 [3]. The drivers are not yet implemented in the second CoRDIA prototype, but Place&Route estimations suggest the area reserved is more than enough for the purpose, even reserving some space for TSV landing pads.
The prototype has been submitted for manufacturing at the end of 2022, and it is foreseen to be tested in spring 2023. Test results will be reported.
[1] A Marras et al Journal of Physics: Conference Series 2380 (2022) 012093
[2] X.Shi et al NIM-A Vol 624, Iss 2, 11 December 2010, Pages 387-391
[3] X. Llopart et al 2022 JINST 17 C01044
