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Proceedings Paper

A CAPD based time-of-flight ranging pixel with wide dynamic range
Author(s): Daniel Van Nieuwenhove; Ward Van der Tempel; Riemer Grootjans; Maarten Kuijk
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Paper Abstract

An in depth view is given of time-of-flight distance sensor and read-out circuit implementations. The sensor is a current assisted photonic demodulator, using majority currents to accelerate generated minority carriers towards the detecting junctions, and combines an efficient mixer with a sensitive detector. Single ended and differential configurations of the structure are illustrated. Measurements show a quantum efficiency of 58%, a DC demodulation contrast of nearly 100% and a contrast of over 40% maintained up till 60 MHz. An improved embodiment, having an extra drain tap to tune sensitivity, is also presented. With this structure automatic gain control and improved dynamic range can be achieved. Measurements demonstrate a controllable sensitivity from maximal to below 1% by changing a sensor control voltage. Secondly design aspects of the read-out circuit are discussed. A circuit with improved background light suppression and dynamic range is explained, called variable transimpedance amplifier. Special low pass filters for in-pixel averaging are presented, having a tuneable cut-off frequency of 10 Hz to 10 kHz and using only 100 μm2. Circuit simulations show a dynamic range of 87 dB, as well as a background light tolerance up to 10 μA. Combining the circuit with a drain tap sensor yields a dynamic range of 127 dB. A standard CMOS 0.35 μm proof of principle prototype pixel, measuring 50 μm x 50 μm and having a 60% fill factor, is presented. Properties, as well as an example image, of a 32x32 CAPD imager are included.

Paper Details

Date Published: 25 April 2008
PDF: 9 pages
Proc. SPIE 7000, Optical and Digital Image Processing, 70000N (25 April 2008); doi: 10.1117/12.781187
Show Author Affiliations
Daniel Van Nieuwenhove, Vrije Univ. Brussel (Belgium)
Ward Van der Tempel, Vrije Univ. Brussel (Belgium)
Riemer Grootjans, Vrije Univ. Brussel (Belgium)
Maarten Kuijk, Vrije Univ. Brussel (Belgium)

Published in SPIE Proceedings Vol. 7000:
Optical and Digital Image Processing
Peter Schelkens; Touradj Ebrahimi; Gabriel Cristóbal; Frédéric Truchetet, Editor(s)

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