Active pixels for image sensing with programmable, high dynamic range

A novel silicon solid-state photodetector pixel structure is presented which exhibits an enhanced dynamic range. This is achieved by subtraction an offset current from the pixel´s photosite while retaining a linear readout characteristic. The offset current can be programmed by a specific programming voltage. This novel circuit is suitable for conventional photodiode sensor architectures as well as for the recently demonstrated active pixel sensor (APS) concepts with improved fixed pattern and readout noise performance. Experimental results from a single pixel test-cell fabricated on a standard 2μ CMOS-process show a programmable offset range of >140 dB with a dynamic range of >50 dB for a given offset current. Arranged in a linear or two-dimensional array, this basic photodetector cell is useful for image sensors in machine vision and optical metrology applications