28 research outputs found
Ultra-Low Power Circuits for Batteryless Energy Harvesting Systems and Thermal Compensation in Resistive In-Memory Computing
No full textEmbedded systems, from wearable health monitors and implantable diagnostics to environmental sensor nodes, are becoming increasingly prevalent in modern life. These platforms are often expected to operate continuously under severe energy constraints, where frequent battery replacement is impractical. To address this, there is a growing need for ultra-low-power (ULP) circuits capable of harvesting ambient energy from sources such as radio frequency (RF) fields, biochemical reactions, and photovoltaic cells. Ensuring stable operation under these limited and varying energy conditions requires circuits with ULP consumption and robust performance under variations. This thesis presents an approach to the design, implementation, and experimental validation of ULP integrated circuits across multiple circuit blocks, tailored for energy-autonomous and flexible systems. The contributions span several key building blocks of energy-harvesting systems, including variation-insensitive voltage and current reference generators, RF-DC converters, low-dropout (LDO) regulators, and switched-capacitor (SC) DC-DC converters with finegrained, arithmetic progression-based voltage scaling. Further, the work introduces thermal compensation techniques to maintain computational accuracy for analog in-memory computing units under varying thermal conditions. The circuits presented in this thesis are designed and fabricated using a conventional CMOS in 65 nm and Pragmatic 600 nm flexible indium gallium zinc oxide (IGZO) based technology using unipolar TFT-based transistors.
Variation-insensitive reference generators form the foundation for reliable biasing across the circuits presented in this work. To address this, the thesis implements amplifier-free, MOS-based voltage and current references that ensure stable operation under varying conditions. A dual-mode, all-NMOS circuit is developed to function both as a voltage reference and a temperature sensor, enabling efficient circuit reuse in energy and area constrained systems. This circuit is further extended to flexible electronics, with a voltage reference designed using IGZO thin-film transistors. For energy regulation, an LDO based on IGZO unipolar transistors is presented, offering efficient voltage regulation under a low quiescent current of 150 nA. An RF-to-DC converter targeting operation in 13.56 MHz is also developed to harvest energy from wireless sources. To support energy sources with variable and degrading outputs, such as biofuel or zinc-air cells, a reconfigurable switched-capacitor DC-DC converter is introduced, with arithmetic progression control of voltage conversion steps of 0.125.
The proposed circuits are implemented for voided fluid volume sensing in smart diapers powered by urine-based energy harvesters. Additionally, voltage regulation using DC-DC converters operating from degrading and decaying energy sources has been designed. The circuits implemented are validated through system-level integration in practical applications. A smart diaper platform powered entirely by harvested urine energy demonstrates the feasibility of fully autonomous operation. Additionally, the thesis addresses thermal variability in analog in-memory computing arrays through two compensation techniques: one using programmable calibration, and another using on-chip thermal sensing for automatic adjustment. The circuits developed in this work enable energy-autonomous operation in batteryless systems and provide robust thermal stability for analog in-memory computing.navigointi mahdollistakuvilla vaihtoehtoiset kuvauksettaulukot saavutettaviastrukturell navigationalternativa textuella beskrivningar för bildertabeller tillgängligastructural navigationalternative textual descriptions for imagestables accessibl
A Compact Untrimmed 48ppm/°C All MOS Current Reference Circuit
No full textFunding Information: The authors are grateful to Academy of Finland for funding this work under the project EHIR (Wireless impulse radio data link powered by energy harvesting). Publisher Copyright: © 2022 IEEE.An ultra-low power and low-cost (area efficient) nano-Ampere current reference circuit designed in a 65 nm technology is presented in this paper: The proposed circuit is a resistorless beta multiplier current reference circuit that uses self cascode composite MOSFETs in triode region. Circuit analysis has been discussed in the paper. The simulated circuit consumes power of 550 nW at a nominal operating voltage of 1.33 V and occupies area of 0.0031 mm2. The design provides a line regulation of 1.9 %/V over an operating voltage range of 1.25 V to 1.4 V. Temperature coefficient (TC) of the circuit at nominal voltage of 1.33 V is 48 ppm/°C for a wide temperature range of-40°C to 85°C. Output current of the circuit at nominal voltage is 104.2 nA with a small process variation of only 4 %.Peer reviewe
A Sub-nW Temperature Invariant Voltage Reference in a Unipolar TFT-based Flexible IC Technology
No full textPublisher Copyright: © 2024 IEEE.Voltage reference circuits are crucial for any mixed-signal circuits, providing PVT (Process, Voltage, Temperature) robust output for the system's stability and accuracy. This paper presents a novel voltage reference circuit implemented in an indium gallium zinc oxide (IGZO) based thin film transistors (TFT) technology, proposing for the first time a sub-nanowatt, area-efficient circuit realized with only a single N-type TFT in a 600 nm technology. The design occupies a minimal area of 27x37 μm2, operates across a broad supply voltage range from 0.5 V to 3 V, and maintains functionality from 0 °C to 100 °C. The circuit has an ultra-low power consumption between 0.75 nW to 1.2 nW while achieving an output voltage of 454 mV with a temperature coefficient (TC) as low as 28.9 ppm/°C. The simulated results, which include process variation, temperature dependence, line sensitivity and power supply rejection ratio measurements, underline the circuit's potential for high-efficiency, low-power applications in next-generation flexible electronics.Peer reviewe
A 99.95% Current Efficient Temperature Invariant All-in-One Reference Circuit on Flexible Substrate
No full textPublisher Copyright: © 2025 IEEE.This work presents a sub-100 nW all-in-one voltage and current reference circuit implemented using 600 nm indium gallium zinc oxide (IGZO) thin-film transistor (TFT) on a flexible substrate. The proposed design integrates both voltage and current references into a single, simple, and compact architecture. By employing NMOS-only devices with negative feedback, the circuit achieves temperature compensation over a temperature range from 10 °C to 100 °C through a stabilized zero temperature coefficient (ZTC) bias point, enhancing the temperature coefficients (TCs). Simulation results demonstrate that the circuit provides a stable reference current of 78.14 nA and a reference voltage of 1.153 V at room temperature (27 °C), with TCs of 99.6 ppm/°C and 263.6 ppm/°C, respectively. The line sensitivities (LS) are 1.276%/V for the current reference and 0.319%/V for the voltage reference over a supply voltage range from 1.5 V to 5 V making it suitable for integration into both flexible electronics and even conventional Si-based CMOS circuits. The circuit achieves a current efficiency of 99.95% and occupies an area of 0.0183Peer reviewe
Flexible RF to DC Converter for Wireless Power Transfer in NFC and Biomedical Systems
No full textPublisher Copyright: © 2024 IEEE.To facilitate the versatile use of flexible energy harvesters, this work discusses the design and characterization of a novel radio frequency (RF) to DC converter built in indium gallium zinc oxide (IGZO) thin film transistor (TFT) technology, developed to meet the energy requirements of near-field communication (NFC) and biomedical applications. The design uses a hybrid topology that combines the efficiency of a cross-coupled converter with the voltage-enhancing capabilities of Dickson charge pumps. This converter is designed to address the challenges of variable RF environments because of its dynamic adjustment technique involving self-biasing resistors and gate voltage-boosting capacitors. The circuit is implemented in a 600 nm TFT technology, and post-layout simulations verify that the circuit can achieve a peak power conversion efficiency (PCE) of 41.5 % at a load resistance of 906 kΩ and exhibiting sensitivity levels as low as -20 dBm. The compact area of 0.0127 mm2 gives this circuit the potential for integration into disposable NFC tags and single-use biomedical devices where efficiency, size, and cost are key factors.Peer reviewe
A 99.95% Current Efficient Temperature Invariant All-in-One Reference Circuit on Flexible Substrate
No full textThis work presents a sub-100 nW all-in-one voltage and current reference circuit implemented using 600 nm indium gallium zinc oxide (IGZO) thin-film transistor (TFT) on a flexible substrate. The proposed design integrates both voltage and current references into a single, simple, and compact architecture. By employing NMOS-only devices with negative feedback, the circuit achieves temperature compensation over a temperature range from 10 °C to 100 °C through a stabilized zero temperature coefficient (ZTC) bias point, enhancing the temperature coefficients (TCs). Simulation results demonstrate that the circuit provides a stable reference current of 78.14 nA and a reference voltage of 1.153 V at room temperature (27 °C), with TCs of 99.6 ppm/°C and 263.6 ppm/°C, respectively. The line sensitivities (LS) are 1.276%/V for the current reference and 0.319%/V for the voltage reference over a supply voltage range from 1.5 V to 5 V making it suitable for integration into both flexible electronics and even conventional Si-based CMOS circuits. The circuit achieves a current efficiency of 99.95% and occupies an area of 0.0183</p
A temperature and process compensation circuit for resistive-based in-memory computing arrays
No full textFunding Information: ACKNOWLEDGMENTS This work is supported by Academy of Finland projects EHIR (grant 13334487) and WHISTLE (grant 332218) Publisher Copyright: © 2023 IEEE.In-Memory Computing (IMC) architectures promise increased energy-efficiency for embedded artificial intelligence. Many IMC circuits rely on analog computation, which is more sensitive to process and temperature variations than digital. Thus, maintaining a suitable computation accuracy may require process and temperature compensation. Focusing on resistive-based IMC architectures, we propose an ultra-low power circuit to compensate for the temperature and process-based non-linearities of resistive computing elements. The proposed circuit, implemented in 65 nm CMOS can provide a temperature coefficient between 10 and 1938 ppm/°C for a wide temperature range (-40°C to 80°C) and output current range (few pA up to 600 nA) at 1.2 V operating voltage. Used in a resistive IMC array, the variation of output currents from each multiply-accumulate (MAC) operation can be reduced by up to 84% to maintain computation accuracy across process and temperature variations.Peer reviewe
Ultra-Low-Power Front-end Design on Flexible IC Technology for Capacitive Sensors
No full textPublisher Copyright: © 2024 IEEE.This paper presents an application-specific integrated circuit (ASIC) front-end, to interface the printed capacitive sensors, using an amorphous Indium-Gallium-Zinc-Oxide (a-IGZO) thin film transistors (TFT) on flexible integrated circuit (FlexIC) technology. A ring oscillator (RO) based front-end sensor interface is designed with 0.024 mm2 area using 600 nm channel length of n-type TFTs consuming 183 nW at a supply voltage of 1 V. It generates output frequency sensitive to the change in the input capacitance of the printed coplanar sensor introduced by the moisture variations. Measurement results show that the front-end ASIC can detect the change in capacitance from 10 pF up to 500 pF of the printed coplanar sensor making it suitable not only for moisture detection but also for the evaluation of voided liquid volumes inside diapers to realize economical, disposable and battery-less Internet of Things (IoT) sensor nodes using green energy harvested from urine.Peer reviewe
An Arithmetic VCR DC–DC Converter for Self-Powered Systems Using Decaying and Degrading Energy Sources
No full textEnergy sources such as biofuel cells, microbial fuel cells, zinc-air batteries, etc., exhibit gradual voltage degradation due to substrate depletion, electrolyte evaporation, and environmental factors, requiring efficient power regulation for continuous operation in energy-constrained IoT sensor nodes. A low-ripple multi-cell switched-capacitor DC-DC converter with arithmetic progression voltage conversion ratio (VCR) change is presented to address this challenge. The design eliminates bulky external load capacitors by implementing dual-stage complementary switching, thereby reducing output ripple while enabling compact integration suitable for miniaturized IoT sensor nodes. A floating N-well stacked MIM-on-MOS capacitor implementation minimizes bottom-plate parasitic losses, improving power conversion efficiency (PCE) across varying VCR modes. The arithmetic progression multi-cell (A-PMC) converter dynamically adjusts VCR transitions in 0.125× increments between 0.5× and 2.0× using a simple finite-state machine (FSM)based control, enabling a gradual increase in VCR w.r.t input voltage decay without complex real-time feedback. Fabricated in a 65nm bulk CMOS process, the design occupies 1.28 mm2, operates across a frequency range of 5 kHz to 250 kHz, and supports input voltages from 0.3 V to 1.8 V. The converter achieves a peak PCE of 88.81% at 2× VCR (93.76% at 1× VCR), with a power density of 0.1565 mW/mm2. The converter’s performance is validated under multiple realistic input decay profiles relevant to IoT applications. The combination of fine-grained VCR control, ripple reduction, and optimized parasitic minimization enhances PCE and stability, making this converter well-suited for energy-harvesting and IoT-compatible applications.</p
TRIM:Thermal Auto-Compensation for Resistive In-Memory Computing
No full textin-memory computing (IMC) has emerged as one of the most promising architectures to efficiently compute artificial intelligence tasks on hardware, particularly deep neural networks (DNNs). IMC can make use of analog computation principles alongside emerging nonvolatile memories (eNVM) technologies, potentially offering several orders of magnitude increased energy efficiency compared to generic processing units. Yet, the use of analog circuitry, potentially integrated with emerging technologies post-processed on top of silicon wafers, increases the susceptibility of hardware to a large spectrum of variations, for instance manufacturing, noise or temperature sensitivity. Hence, this susceptibility can hamper the large-scale deployment of IMC circuits into the market. To tackle the reliability of analog resistive-based IMC circuits regarding temperature variations, this article presents TRIM, a thermal on-chip auto-compensation method aimed at fully calibrating first-order temperature effects. TRIM is designed to maintain the computational accuracy of IMC cores in DNN applications over a wide temperature range, while being highly scalable and adaptable. In essence, the temperature compensation is realized through a complementary-to-absolute-temperature (CTAT) voltage reference integrated inside a voltage regulator and applied at the zero reference node of a multiplying digital-to-analog converter (MDAC), eliminating the need for external circuits or look-up table. The proposed methodology is demonstrated on a proof-of-concept 65 nm CMOS resistive IMC column. Measurement results showcase that the proof-of-concept auto-compensation system significantly enhances inference and multiply-and-accumulate (MAC) operation accuracy of any first-order resistive crossbar column, achieving inference accuracy recovery of 100% over a temperature range of –20 °C to 60 °C and a 91.3% improvement in MAC operation accuracy, with an area overhead of 2% and power overhead of < 0.02%.</p
