A 100x100 CMOS SPAD Array with In-Pixel Correlation Techniques for Fast Quantum Ghost Imaging Applications

In this paper, a 100x100 CMOS Single Photon Avalanche Diode (SPAD) array designed for quantum imaging applications requiring synchronization with an external unpredictable and aperiodic trigger is presented. The targeted application takes advantage of non-classical quantum states of light to achieve quantum ghost imaging in the middle-infrared (MIR) up to 7 $\mu \mathrm{m}$ wavelength by detecting the corresponding entangled photons in the visible spectrum with the SPAD imager. For this purpose, a SPAD array with in-pixel backward-looking temporal correlation capabilities has been implemented to spatially resolve the entangled photons in a ghost imaging setup. The correlation is performed through a pixel-wise asynchronous delayed time window, whose width can be tuned to maximize the correlation efficiency. Two pixel variants, without and with resource sharing, have been designed: the resulting imager has been implemented in a 110 nm CIS FSI technology, achieving a correlation window width between 2 ns and 27 ns and a delay range between 5 ns and 40 ns, with 17 $\mu \mathrm{m}$ pixel pitch and fill-factor of 19.3% and 31.3%. A smart readout architecture has been implemented to improve the acquisition duty cycle, given the expected sparsity of the detected events.