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1. An efficient DC‐DC converter for inductive power transfer in low‐power sensor applications

   https://doi.org/10.1002/cta.3285  

   Lu, Ruikuan; Hossain, Md. Kamal; Alexander, J. Iwan; Massoud, Yehia; Haider, Mohammad R. (April 2022, International Journal of Circuit Theory and Applications)

   Summary Inductive power transfer has become an emerging technology for its significant benefits in many applications, including mobile phones, laptops, electric vehicles, implanted bio‐sensors, and internet of things (IoT) devices. In modern applications, a direct current–direct current (DC–DC) converter is one of the essential components to regulate the output supply voltage for achieving the desired characteristics, that is, steady voltage with lower peak ripples. This paper presents a switched‐capacitor (SC) DC–DC converter using complementary architecture to provide a regulated DC voltage with an increased dynamic response. The proposed topology enhances the converter efficiency by decreasing the equivalent output resistance to half by connecting two symmetric SC single ladder converters. The proposed converter is designed using the standard 130‐nm BiCMOS process. The results show that the proposed architecture produces 327‐mV DC output with a rise time of 60.1 ns and consumes 3.449‐nW power for 1.0‐V DC supply. The output settling time is 43.6% lower than the single‐stage SC DC–DC converter with an input frequency of 200 MHz. The comparison results show that the proposed converter has a higher power conversion efficiency of 93.87%and a lower power density of 0.57 mW/mm²compared to the existing works. 

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2. Self-Powered Motion Tracking Sensor Integrated with Low-Power CMOS Circuitry

   https://doi.org/10.1109/ISCAS51556.2021.9401440  

   Tasneem, Nishat T.; Biswas, Dipon K.; Mahbub, Ifana; Adhikari, Pashupati R.; Reid, Russell (May 2021, 2021 IEEE International Symposium on Circuits and Systems (ISCAS))

   null (Ed.)

   This paper presents a motion-sensing device with the capability of harvesting energy from low-frequency motion activities that can be utilized for long-term human health monitoring. The energy harvester used in the proposed motion sensor is based on the mechanical modulation of liquid on an insulated electrode, which utilizes a technique referred to as reverse electrowetting-on-dielectric (REWOD). The generated AC signal from the REWOD is rectified to a DC voltage using a Schottky diode-based rectifier and boosted subsequently with the help of a linear charge-pump circuit and a low-dropout regulator (LDO). The constant DC voltage from the LDO (1.8 V) powers the motion-sensing read-out circuitry, which converts the generated charge into a proportional output voltage using a charge amplifier. After amplification of the motion data, a 5-bit SAR-ADC (successive-approximation register ADC) digitizes the signal to be transmitted to a remote receiver. Both the CMOS energy harvester circuit including the rectifier, the charge-pump circuit, the LDO, and the read-out circuit including the charge amplifier, and the ADC is designed in the standard 180 nm CMOS technology. The amplified amplitude goes up to 1.76 V at 10 Hz motion frequency, following linearity with respect to the frequency. The generated DC voltage from the REWOD after the rectifier and the charge-pump is found to be 2.4 V, having the voltage conversion ratio (VCR) as 32.65% at 10 Hz of motion frequency. The power conversion efficiency (PCE) of the rectifier is simulated as high as 68.57% at 10 Hz. The LDO provides the power supply voltage of 1.8 V to the read-out circuit. The energy harvester demonstrates a linear relationship between the frequency of motion and the generated output power, making it suitable as a self-powered wearable motion sensor. 

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3. A ±0.5-mV-Minimum-Input DC-DC Converter With Stepwise Adiabatic Gate-Drive and Efficient Timing Control for Thermoelectric Energy Harvesting

   https://doi.org/10.1109/TCSI.2022.3219402  

   Carlson, Eric J.; Smith, Joshua R. (February 2023, IEEE Transactions on Circuits and Systems I: Regular Papers)

   This paper presents a step-up DC-DC converter that uses a stepwise gate-drive technique to reduce the power FET gate-drive energy by 82%, allowing positive efficiency down to an input voltage of ±0.5 mV—the lowest input voltage ever achieved for a DC-DC converter as far as we know. Below ±0.5 mV the converter automatically hibernates, reducing quiescent power consumption to just 255 pW. The converter has an efficiency of 63% at ±1 mV and 84% at ±6 mV. The input impedance is programmable from 1 Ω to 600 Ω to achieve maximum power extraction. A novel delay line circuit controls the stepwise gatedrive timing, programmable input impedance, and hibernation behavior. Bipolar input voltage is supported by using a flyback converter topology with two secondary windings. A generated power good signal enables the load when the output voltage has charged above 2.7 V and disables when the output voltage has discharged below 2.5 V. The DC-DC converter was used in a thermoelectric energy harvesting system that effectively harvests energy from small indoor temperature fluctuations of less than 1°C. Also, an analytical model with unprecedented accuracy of the stepwise gate-drive energy is presented. 

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4. Highly Efficient Rectifier and DC-DC Converter Designed in 180 nm CMOS Process for Ultra-Low Frequency Energy Harvesting Applications

   https://doi.org/10.1109/DCAS51144.2020.9330671  

   Gunti, Avinash; Biswas, Dipon K.; Mahbub, Ifana; Adhikari, Pashupati R.; Reid, Russell C. (November 2020, 2020 IEEE 14th Dallas Circuits and Systems Conference (DCAS))

   null (Ed.)

   This paper presents the integration of an AC-DC rectifier and a DC-DC boost converter circuit designed in 180 nm CMOS process for ultra-low frequency (<; 10 Hz) energy harvesting applications. The proposed rectifier is a very low voltage CMOS rectifier circuit that rectifies the low-frequency signal of 100-250 mV amplitude and 1-10 Hz frequency into DC voltage. In this work, the energy is harvested from the REWOD (reverse electrowetting-on-dielectric) generator, which is a reverse electrowetting technique that converts mechanical vibrations to electrical energy. The objective is to develop a REWOD-based self-powered motion (such as walking, running, jogging, etc.) tracking sensors that can be worn, thus harvesting energy from regular activities. To this end, the proposed circuits are designed in such a way that the output from the REWOD is rectified and regulated using a DC-DC converter which is a 5-stage cross-coupled switching circuit. Simulation results show a voltage range of 1.1 V-2.1 V, i.e., 850-1200% voltage conversion efficiency (VCE) and 30% power conversion efficiency (PCE) for low input signal in the range 100-250 mV in the low-frequency range. This performance verifies the integration of the rectifier and DC-DC boost converter which makes it highly suitable for various motion-based energy harvesting applications. 

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5. A Hybrid Cockcroft-Walton / Dickson Multiplier for High Voltage Generation

   https://doi.org/10.1109/TPEL.2019.2929167  

   Park, Sanghyeon; Yang, Jun; Rivas Davila, Juan Manuel (July 2019, IEEE Transactions on Power Electronics)

   This paper presents a voltage multiplier topology that is a hybrid between a Cockcroft-Walton multiplier and a Dickson charge pump. The Cockcroft-Walton structure exhibits significant output voltage drop under load as the number of multiplier stage increases. This is because all coupling capacitors are connected in series. Dickson charge pump mitigates this issue by connecting all capacitors in parallel. But this solution comes at the expense of large capacitor voltage stress at the last multiplier stage. The proposed hybrid structure arranges some capacitors in parallel and others in series, thereby achieving low output voltage drop and low capacitor voltage stress at the same time. We develop a model that predicts hybrid multiplier's performance and validate it experimentally. We also demonstrate a 60 V-to-2.25 kV dc-dc converter based on a 16-stage hybrid voltage multiplier which achieves a voltage gain of 12.8 while keeping the highest capacitor voltage stress to 660 V. 

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