University of Twente Student Theses


Inhibition of mobile phone cameras

Kraakman, J. (2021) Inhibition of mobile phone cameras.

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Abstract:The pixel of a CMOS camera consists of a photodiode, a potential well, an amplifier and a reset/readout mechanism. This can be seen in figure \ref{fig:CMOSpix}. When a photon strikes the photodiode an electron is generated and stored in the potential well. The potential well is connected to a source follower which acts as a buffer. When the pixel has been read out, the well will be emptied and the pixel is ready to start counting photons again. With this the camera can detect brightness but no color yet. For this a Bayer filter is used which can be seen in figure \ref{fig:bayerf}. This filter is a grid that consists of red, green and blue light filters and makes each pixel responsible for one color. The reason there are more green filters is to make the color sensitivity of the camera more closely resemble the sensitivity of the human eye, which will be discussed later. The sensitivity can of course also be corrected for with amplification and this is actually still used to do the last fine tuning \cite{CMOSexplan}. However, by using the Bayer filter this way, less amplification is needed and thus less noise is being amplified as well. Another function of the amplifiers are to account for different lighting conditions. Since mobile phones do not have a physical shutter, the pixels are constantly exposed. So to account for the lack/abundance of light the amplification is changed. Lastly there is the microlens, this is used to capture light that would otherwise be lost because it would fall on the circuitry.
Item Type:Essay (Bachelor)
Faculty:EEMCS: Electrical Engineering, Mathematics and Computer Science
Subject:50 technical science in general
Programme:Electrical Engineering BSc (56953)
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