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A high fill-factor self-buffered active pixel sensor and a tunable injection current compensation architecture for high dynamic range imager are proposed for scaled standard CMOS technology. The new cell, including a photo diode formed by n-well and p-type substrate and an one-transistor output buffer, shows enhanced characteristics in output voltage swing and sensitivity compared with conventional APS. The imager can achieve fill-factor of 55%, sensitivity of 3.4 V/sec-lux, and large output swing of 2.2 V at VDD=3.3 V for 0.25-μm CMOS technology. In addition, the proposed tunable injection current compensation architecture can improve dynamic range by as much as 40 dB and can be tailor designed to meet various application specifications. A dynamic range of up to 120 dB is projected by simulation results. Experimental results of the new structure, as well as simulated design of the circuit, are presented.