Linear-logarithmic image sensor with low noise and no flickers

This paper proposes and demonstrates a linear-logarithmic image sensor that can operate in both the linear and logarithmic modes, and exhibits low noise and no flickers. Its pixel is composed of one buried-photodiode, five n-channel MOS transistors, two p-channel MOS transistors, and one capacitor. During the linear mode operation, the pixel behaves the same as the four-transistor one, offering a low dark current and low noise. Also, in the logarithmic mode, it operates in an integrating manner in contrast to the majority of logarithmic-response CMOS image sensors that operate in a continuous manner. Thus it has no flickers and can calibrate the fixed pattern noise using the reference level. A wide dynamic range of 190 dB has been confirmed with a 256 x 256-pixel image sensor employing this novel pixel architecture.