A Linear-Logarithmic CMOS Image Sensor With Adjustable Dynamic Range

A new pixel structure is proposed for wide dynamic range CMOS image sensors. A pixel based on a three-transistor active pixel sensor has two linear responses and a logarithmic response using additional circuits. The photogate surrounding the n + /p-sub photodiode exists for the second linear response. The logarithmic response is due to the biased MOS cascode. The proposed pixel was designed and fabricated using a 0.35- $\mu \text{m}$ 2-poly 4-metal standard CMOS process. The dynamic range of the pixel is higher than 106 dB. A test chip with a pixel pitch of $10 \times 10~\mu \text{m}^{2}$ and a $160 \times 120$ pixel array is evaluated.