A SPAD-based 3D imager with in-pixel TDC for 145ps-accuracy ToF measurement

I. Vornicu; R. Carmona-Galán; Á. Rodríguez-Vázquez

doi:10.1117/12.2078777

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13 March 2015 A SPAD-based 3D imager with in-pixel TDC for 145ps-accuracy ToF measurement

I. Vornicu, R. Carmona-Galán, Á. Rodríguez-Vázquez

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Proceedings Volume 9403, Image Sensors and Imaging Systems 2015; 94030I (2015) https://doi.org/10.1117/12.2078777
Event: SPIE/IS&T Electronic Imaging, 2015, San Francisco, California, United States

Abstract

The design and measurements of a CMOS 64 × 64 Single-Photon Avalanche-Diode (SPAD) array with in-pixel Time-to-Digital Converter (TDC) are presented. This paper thoroughly describes the imager at architectural and circuit level with particular emphasis on the characterization of the SPAD-detector ensemble. It is aimed to 2D imaging and 3D image reconstruction in low light environments. It has been fabricated in a standard 0.18μm CMOS process, i. e. without high voltage or low noise features. In these circumstances, we are facing a high number of dark counts and low photon detection efficiency. Several techniques have been applied to ensure proper functionality, namely: i) time-gated SPAD front-end with fast active-quenching/recharge circuit featuring tunable dead-time, ii) reverse start-stop scheme, iii) programmable time resolution of the TDC based on a novel pseudo-differential voltage controlled ring oscillator with fast start-up, iv) a global calibration scheme against temperature and process variation. Measurements results of individual SPAD-TDC ensemble jitter, array uniformity and time resolution programmability are also provided.

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I. Vornicu, R. Carmona-Galán, and Á. Rodríguez-Vázquez "A SPAD-based 3D imager with in-pixel TDC for 145ps-accuracy ToF measurement", Proc. SPIE 9403, Image Sensors and Imaging Systems 2015, 94030I (13 March 2015); https://doi.org/10.1117/12.2078777

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