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In this paper, we present an ultra-low-power current-mode image sensor with energy harvesting capability. By biasing the in-pixel transconductance amplifier in triode region and using a pipelined 9-bit current-mode analog-to-digital converter (ADC), a power consumption as low as 84 pW/frame per pixel is achieved. Besides the ultra-low-power feature, the proposed 6T pixel can also be used as a solar cell by reconfiguring the in-pixel P+/Nwell photodiode, which can generate several micro watt power at Klux illumination levels. As a result, this energy harvesting imager is very suitable for wireless image sensor network applications. The test chip with a 128 × 96 pixel array resolution is fabricated using a 0.35 μ m CMOS technology. The random noise and the fixed pattern noise (FPN) in dark are 0.4% and 1%, respectively. In the energy harvesting mode, 4.85 μW power can be harvested using the reconfigurable pixel array.
Date of Publication: April 2012