Linear–Logarithmic CMOS Pixel With Tunable Dynamic Range

Abstract

A CMOS pixel with linear-logarithmic response and programmable dynamic range (DR), based on a tunable transition point, has purposely been designed for endoscopic applications. A theoretical model of the pixel was developed and validated. A chip with a 100×100 pixel array and a 12-b digital output was fabricated in a 0.35-μm technology and was fully tested, thus demonstrating state-of-the-art performance in terms of DR and noise. Intraframe DR proved to be extendable to more than 110 dB through a logarithmic compression of the signal in the light irradiation power density (LIPD) range. The measured temporal noise (pixel noise) was less than 0.22% over the full range. The architecture presented limited fixed pattern noise (FPN) due to the scheme adopted, which allowed its correction over the full signal range: FPN was 0.83% (1.37%) in the linear (logarithmic) region. Although the test chip was designed mainly for endoscopic applications, the technology may also be applied to other fields, e.g., robotics, security and industrial automation, whenever high DR is a crucial feature.