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1. 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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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 Novel Energy-Efficient Sinusoidal Power Clocking-Based Writing Circuitry for the Hybrid CMOS/MTJ Architecture

   https://doi.org/10.1109/TMAG.2024.3430120  

   Yang, Wu; Degada, Amit; Thapliyal, Himanshu (September 2024, IEEE Transactions on Magnetics)

   Spin transfer torque magnetic random access memory (STT-MRAM) offers a promising solution for low-power and high-density memory due to its compatibility with CMOS, higher density, scalable nature, and non-volatility. However, the higher energy required to write bit cells has remained a key challenge for its adaptation into battery-operated smart handheld devices. The existing low-energy writing solutions require additional complex control logic mechanisms, further constraining the available area. In this research, we propose a solution to design energy-efficient write circuits by incorporating two techniques together. First, we propose the sinusoidal power clocking mechanism replacing the DC power supply in the conventional CMOS design. Second, we propose three lookup table (LUT)-based control logic circuits and one write circuit to reduce the area and further minimize energy dissipation. The experimental results are verified over the case study implementations of 4×4 STT-MRAM macro designed using bit cell configurations: i) one transistor and one magnetic tunnel junction (MTJ) (1T-1MTJ) and ii) four transistors and two MTJs (4T-2MTJ). The post-layout simulation for the frequency range from 250 kHz to 6.25 MHz shows that the write circuit, which uses the proposed LUT-based control logic circuits and a write driver with a sinusoidal power supply, achieves more than a 65.05% average energy saving compared to the CMOS counterpart. Furthermore, the write circuit, which uses the proposed 6T write driver with the sinusoidal power supply, shows an improvement in energy saving by more than 70.60% compared to the CMOS counterpart. We also verified that the energy-saving performance remains relatively consistent with the change in temperature and the tunneling magnetoresistance (TMR) ratio. 

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4. Generalized Architecture of a GaN-Based Modular Multiport Multilevel Flying Capacitor Converter

   https://doi.org/10.1109/TPEL.2023.3269800  

   Tamasas Elrais, Mohamed; Safayatullah, Md; Batarseh, Issa (January 2023, IEEE Transactions on Power Electronics)

   This paper proposes a generalized Gallium Nitride (GaN) based modular multiport multilevel flying capacitor architecture. In other words, the attractive flying capacitor multilevel (FCML) design and the full-bridge unfolding circuit are employed to develop a multiport multilevel converter architecture that fits various applications. Each module can be designed to contain any combination of AC and DC ports connected through DC-to-DC and DC-to-AC power conversion paths. These conversion paths are FCML topologies that can be designed with any number of levels; the DC-to-AC paths incorporate the full-bridge unfolding circuit. Two example prototypes with open-loop control, three-port and four-port, have verified this generalized architecture. A single module 3 kW three-port four-level prototype with two DC ports and an AC port has achieved a compact size of 11.6 in 3 (4.8 in ×4.3 in × 0.56 in) and a high power density of 258.6 W/in 3 . The three ports are connected through DC-to-AC and DC-to-DC paths that have achieved peak efficiencies of 98.2% and 99.43%, respectively. The total harmonic distortion (THD) of the AC port's voltage and current are 1.26% and 1.23%, respectively. It operates at a high switching frequency of 120 kHz because of the GaN switches and has an actual frequency (inductor's ripple frequency) of 360 kHz thanks to the frequency multiplication effect of the FCML. The four-port prototype contains three DC ports and an AC port and achieved similar high figures of merit. These experimental results of the two prototypes of high efficiency, power density, and compact size are presented in this article and highlight this architecture's promising potential. The choice of the number of modules, ports, and levels depends on the application and its specification; therefore, this proposed generalized structure may serve as a reference design approach for various applications of interest. 

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5. Modeling and Optimization of Directly Modulated Piezoelectric Micromachined Ultrasonic Transducers

   https://doi.org/10.3390/s21010157  

   Pop, Flavius; Herrera, Bernard; Cassella, Cristian; Rinaldi, Matteo (January 2021, Sensors)

   The present work details a novel approach to increase the transmitting sensitivity of piezoelectric micromachined ultrasonic transducer arrays and performing the direct modulation of digital information on the same device. The direct modulation system can reach 3× higher signal-to-noise ratio level and 3× higher communication range (from 6.2 cm boosted to 18.6 cm) when compared to more traditional continuous wave drive at the same energy consumption levels. When compared for the same transmission performance, the direct modulation consumes 80% less energy compared to the continues wave. The increased performance is achieved with a switching circuit that allows to generate a short high-AC voltage on the ultrasonic array, by using an LC tank and a bipolar junction transistor, starting with a low-DC voltage, making it CMOS-compatible. Since the modulation signal can directly be formed by the transmitted bits (on/off keying encoding) this also serve as the modulation for the data itself, hence direct modulation. The working principle of the circuit is described, optimization is performed relative to several circuital parameters and a high-performance experimental application is demonstrated. 

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