A Linear-Logarithmic CMOS Image Sensor With Adjustable Dynamic Range

Abstract

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 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> /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-μm 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 × 10 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and a 160 × 120 pixel array is evaluated.