Implantable technologies are becoming more widespread for biomedical applications that include physical identification, health diagnosis, monitoring, recording, and treatment of human physiological traits. However, energy harvesting and power generation beneath the human tissue are still a major challenge. In this regard, self‐powered implantable devices that scavenge energy from the human body are attractive for long‐term monitoring of human physiological traits. Thanks to advancements in material science and nanotechnology, energy harvesting techniques that rely on piezoelectricity, thermoelectricity, biofuel, and radio frequency power transfer are emerging. However, all these techniques suffer from limitations that include low power output, bulky size, or low efficiency. Photovoltaic (PV) energy conversion is one of the most promising candidates for implantable applications due to their higher‐power conversion efficiencies and small footprint. Herein, the latest implantable energy harvesting technologies are surveyed. A comparison between the different state‐of‐the‐art power harvesting methods is also provided. Finally, recommendations are provided regarding the feasibility of PV cells as an in vivo energy harvester, with an emphasis on skin penetration, fabrication, encapsulation, durability, biocompatibility, and power management.

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For better area and power efficiencies, rail-to-railoutput single-stage amplifiers are a potential replacement of their multi-stage counterparts, especially for display applications that entail massive buffer amplifiers in their column drivers. This paper describes a nested-current-mirror (NCM) technique for a single-stage amplifier to achieve substantial enhancements of DC gain, gain-bandwidth product (GBW) and slew rate (SR). Specifically, NCM is customizable for different mirror steps, and sub mirror ratios, to balance the performance metrics and capacitive-load ( ) drivability, avoiding any compensation passives while preserving a rail-to-rail output swing. Analytical treatments of the NCM technique in terms of performance limits and robustness reveal that the NCM amplifier can surpass the fundamental power-efficiency limit set by the basic differential-pair (DP) amplifier. Two prototypes, 3-step and 4-step NCM amplifiers, were fabricated in 0.18 m CMOS for systematic comparison with the DP amplifier. The former represents a robust design exhibiting 72 dB DC gain and 0.0028-0.27 MHz GBW over 0.15-15 nF with 80 phase margin (PM). The latter embodies an aggressive design attaining 84 dB DC gain and 0.013-1.24 MHz GBW over 0.15-15 nF with 62 PM. All amplifiers were sized for the same area (0.0013 mm ) and power (3.6 W).Index Terms-Area efficiency, CMOS, current mirror, DC gain, differential-pair (DP) amplifier, frequency compensation, gain-bandwidth product (GBW), low temperature polysilicon LCD, multi-stage amplifier, nested current mirror, rail-to-rail output swing, single-stage amplifier, slew rate (SR), stability.

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In this paper, an ultra-compact single-chip solar energy harvesting IC using on-chip solar cell for biomedical implant applications is presented. By employing an on-chip charge pump with parallel connected photodiodes, a 3.5 × efficiency improvement can be achieved when compared with the conventional stacked photodiode approach to boost the harvested voltage while preserving a single-chip solution. A photodiode-assisted dual startup circuit (PDSC) is also proposed to improve the area efficiency and increase the startup speed by 77%. By employing an auxiliary charge pump (AQP) using zero threshold voltage (ZVT) devices in parallel with the main charge pump, a low startup voltage of 0.25 V is obtained while minimizing the reversion loss. A 4 V gate drive voltage is utilized to reduce the conduction loss. Systematic charge pump and solar cell area optimization is also introduced to improve the energy harvesting efficiency. The proposed system is implemented in a standard 0.18- [Formula: see text] CMOS technology and occupies an active area of 1.54 [Formula: see text]. Measurement results show that the on-chip charge pump can achieve a maximum efficiency of 67%. With an incident power of 1.22 [Formula: see text] from a halogen light source, the proposed energy harvesting IC can deliver an output power of 1.65 [Formula: see text] at 64% charge pump efficiency. The chip prototype is also verified using in-vitro experiment.

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