Time-to-digital converter based on analog time expansion for 3D time-of-flight cameras

Muhammad Tanveer; Ilkka Nissinen; Jan Nissinen; Juha Kostamovaara; Johan Borg; Jonny Johansson

doi:10.1117/12.2036539

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4 March 2014 Time-to-digital converter based on analog time expansion for 3D time-of-flight cameras

Muhammad Tanveer, Ilkka Nissinen, Jan Nissinen, Juha Kostamovaara, Johan Borg, Jonny Johansson

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Proceedings Volume 9022, Image Sensors and Imaging Systems 2014; 90220A (2014) https://doi.org/10.1117/12.2036539
Event: IS&T/SPIE Electronic Imaging, 2014, San Francisco, California, United States

Abstract

This paper presents an architecture and achievable performance for a time-to-digital converter, for 3D time-of-flight cameras. This design is partitioned in two levels. In the first level, an analog time expansion, where the time interval to be measured is stretched by a factor k, is achieved by charging a capacitor with current I, followed by discharging the capacitor with a current I/k. In the second level, the final time to digital conversion is performed by a global gated ring oscillator based time-to-digital converter. The performance can be increased by exploiting its properties of intrinsic scrambling of quantization noise and mismatch error, and first order noise shaping. The stretched time interval is measured by counting full clock cycles and storing the states of nine phases of the gated ring oscillator. The frequency of the gated ring oscillator is approximately 131 MHz, and an appropriate stretch factor k, can give a resolution of ≈ 57 ps. The combined low nonlinearity of the time stretcher and the gated ring oscillator-based time-to-digital converter can achieve a distance resolution of a few centimeters with low power consumption and small area occupation. The carefully optimized circuit configuration achieved by using an edge aligner, the time amplification property and the gated ring oscillator-based time-to-digital converter may lead to a compact, low power single photon configuration for 3D time-of-flight cameras, aimed for a measurement range of 10 meters.

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Muhammad Tanveer, Ilkka Nissinen, Jan Nissinen, Juha Kostamovaara, Johan Borg, and Jonny Johansson "Time-to-digital converter based on analog time expansion for 3D time-of-flight cameras", Proc. SPIE 9022, Image Sensors and Imaging Systems 2014, 90220A (4 March 2014); https://doi.org/10.1117/12.2036539

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