Oxford University Thesis on Log Sensors

Oxford University, UK, publishes a PhD Thesis "Integrating logarithmic wide dynamic range CMOS image sensors" by Mus'ab B Shaharom:

"Conventional CMOS image sensors with a logarithmic response attempt to address the limited dynamic range of the linear digital image sensors by exploiting the subthreshold operation of a transistor in a pixel. This results in CMOS pixels that are able to capture light intensities of more than six decades (120 dB). However, the approach comes at the expense of high fixed pattern noise (FPN) and slow response.

The work presented in this thesis describes a five all nMOS transistor (5T) pixel architecture that aims to achieve wide dynamic range. This feature is obtained using a time-varying reference voltage that is applied to one of the transistors of the pixel. The reference voltage varies in a logarithmic fashion in order to modulate the effective integration time of the pixel."