Paper
29 April 2016 A logarithmic low dark current CMOS pixel
Alessandro Michel Brunetti, Bhaskar Choubey
Author Affiliations +
Abstract
High dynamic range pixels are required in a number of automotive and scientific applications. CMOS pixels provide different approaches to achieve this. However, these suffer from poor performance under low light conditions due to inherently high leakage current that is present in CMOS processes, also known as dark current. The typical approach to reduce this dark current involves process modifications. Nevertheless, energy considerations suggest that the leakage current will be close to zero at a close to zero voltage on the photodiode. Hence, the reduction in dark current can be achieved by forcing a zero voltage across the photodiode. In this paper, a novel logarithmic CMOS pixel design capable of reducing dark current without any process modifications is proposed. This pixel is also able to produce a wide dynamic range response. This circuit utilizes two current mirrors to force the in-pixel photodiode at a close to zero voltage. Additionally, a bias voltage is used to reduce a higher order effect known as Drain Induced Barrier Lowering (DIBL). In fact, the contribution of this effect can be compensated by increasing the body effect. In this paper, we studied the consequences of a negative bias voltage applied to the body of the current mirror pair to compensate for the DIBL effect thereby achieving a very small voltage drop on the photodiode and consequently, a higher sensitivity in low light conditions.
© (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Alessandro Michel Brunetti and Bhaskar Choubey "A logarithmic low dark current CMOS pixel", Proc. SPIE 9899, Optical Sensing and Detection IV, 98990C (29 April 2016); https://doi.org/10.1117/12.2227795
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KEYWORDS
Photodiodes

Transistors

Diodes

Doping

High dynamic range imaging

CMOS technology

Device simulation

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