Abstract
An ultra-low power CMOS image sensor with on-chip energy harvesting and power management capability is introduced in this paper. The photodiode pixel array can not only capture images but also harvest solar energy. As such, the CMOS image sensor chip is able to switch between imaging and harvesting modes towards self-power operation. Moreover, an on-chip maximum power point tracking (MPPT)-based power management system (PMS) is designed for the dual-mode image sensor to further improve the energy efficiency. A new isolated P-well energy harvesting and imaging (EHI) pixel with very high fill factor is introduced. Several ultra-low power design techniques such as reset and select boosting techniques have been utilized to maintain a wide pixel dynamic range. The chip was designed and fabricated in a 1.8 V, 1P6M 0.18 µm CMOS process. Total power consumption of the imager is 6.53 µW for a 96 × 96 pixel array with 1 V supply and 5 fps frame rate. Up to 30 μW of power could be generated by the new EHI pixels. The PMS is capable of providing 3× the power required during imaging mode with 50% efficiency allowing energy autonomous operation with a 72.5% duty cycle.
Highlights
CMOS image sensors (CISs) have replaced charge-coupled devices (CCD) in most applications due to their low power consumption, high speed, and low cost
Since most CISs operate in illuminated environments, photovoltaic (PV) energy harvesting is the natural choice among all the different kinds of energy harvesters
The power management system (PMS) running a low-power maximum power point tracking (MPPT) algorithm was integrated with a dual-mode CIS that contains new, highly efficient energy harvesting and imaging (EHI) pixels and ultra-low power readout electronics
Summary
CMOS image sensors (CISs) have replaced charge-coupled devices (CCD) in most applications due to their low power consumption, high speed, and low cost. Low-power consumption is a critical requirement that enables standalone operation of sensors and systems in isolated environments for extended durations. Better energy harvesting efficiency was achieved in EHI by decoupling the anode of the energy harvesting photodiode from pixel transistors and other loss paths. High power consumption of readout electronics and low energy harvesting capability of the EHI structure made it impossible to attain self-powered operation. The first energy harvesting type CIS design with integrated power management system (PMS) is introduced. The PMS running a low-power maximum power point tracking (MPPT) algorithm was integrated with a dual-mode CIS that contains new, highly efficient EHI pixels and ultra-low power readout electronics.
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