An auto-switched mode CMOS image sensor for high dynamic range scientific imaging applications

This paper presents a CMOS image sensor with auto-switched mode readout architecture for high throughput and high dynamic range scientific imaging applications. The proposed readout circuit compares background illumination with a threshold level and automatically adjusts the pixel array to operate in either linear or logarithmic mode by feeding back a mode switching control signal. This novel readout architecture allows simultaneous linear-logarithmic operation of each pixel, resulting in direct readout of image sequence covering a dynamic range of 121 dB. A chip consisting of 16 times 16 8-T pixel array and the proposed readout circuit has been designed and fabricated using AMI 0.5 mum technology. The chip has been verified for imaging clusters of nano particles (CoFe₂O₄) illuminated using bright green LED. Experiment results confirm high dynamic range performance due to linear-logarithmic auto-switched mode operation.