A0.5~1.2V CMOS DPS For Bionic Human Eye In65nm CMOS Technology

With the continuous scaling of CMOS technologies which has entered the deepsubmicron regime, the low supply voltage and an increasing noise floor of CMOSactive pixel sensor (APS) lead to poor signal-to-noise ratio (SNR), dynamic range(DR). So the reduced supply voltage places a major limit on the ability of a CMOSAPS to achieve charge-coupled device (CCD)-comparable DR. However, technologyscaling now allows many devices to be incorporated at the pixel level. A digital pixelsensor (DPS), which performs the analog-to-digital conversion (ADC) and memory atthe pixel level, DR is no longer limited by the power-supply rails, has become thecutting edge in the field of image sensor development.In this paper, a CMOS DPS based on pulse width modulation (PWM) scheme isproposed to overcome the restriction of low supply voltage imposed by device scalingtrend. The pixel operates with a dynamic current comparison scheme to avoid usingcomplex in-pixel comparator and can be work under low power supply;The featuresof human eyes, which are wide DR and logarithmic response, are realized byadjusting clock frequency for different illumination, and DR is further extended due toincreasing the maximum detectable photocurrent and lowering the minimumdetectable photocurrent; With the pixel level ADC and SRAM, pixel array canimplement global reset and exposure, so that the designed DPS can achieve a highframe rate; By adjusting the slope of ramp current, the sensitivity at low illuminationregime can be adjusted, which will make the DPS have a broader application fields.The DPS designed in a standard65nm CMOS technology, each pixel contains aphoto-diode, an11-bit in-pixel SRAM and other11transistors, and occupies an areaof7μm×7μm, with a fill factor of31.3%. Simulation results show that this pixel canwork at a supply voltage as low as0.5V~1.2V with120dB DR and80dB lineardynamic range. The properties of high DR and logarithmic response make theproposed DPS be capable of human eye. And frame rate achieves246fps with640×480pixel array.