Sensing systems such as biomedical implants, infrastructure monitoring systems, and military surveillance units are constrained to consume only picowatts to nanowatts in standby and active mode, ...respectively. This tight power budget places ultra-low power demands on all building blocks in the systems. This work proposes a voltage reference for use in such ultra-low power systems, referred to as the 2T voltage reference, which has been demonstrated in silicon across three CMOS technologies. Prototype chips in 0.13 μm show a temperature coefficient of 16.9 ppm/°C (best) and line sensitivity of 0.033%/V, while consuming 2.22 pW in 1350 μm 2 . The lowest functional V dd 0.5 V. The proposed design improves energy efficiency by 2 to 3 orders of magnitude while exhibiting better line sensitivity and temperature coefficient in less area, compared to other nanowatt voltage references. For process spread analysis, 49 dies are measured across two runs, showing the design exhibits comparable spreads in TC and output voltage to existing voltage references in the literature. Digital trimming is demonstrated, and assisted one temperature point digital trimming, guided by initial samples with two temperature point trimming, enables TC <; 50 ppm/°C and ±0.35% output precision across all 25 dies. Ease of technology portability is demonstrated with silicon measurement results in 65 nm, 0.13 μm, and 0.18 μm CMOS technologies.
This paper presents a fully integrated energy harvester that maintains >35% end-to-end efficiency when harvesting from a 0.84 mm 2 solar cell in low light condition of 260 lux, converting 7 nW input ...power from 250 mV to 4 V. Newly proposed self-oscillating switched-capacitor (SC) DC-DC voltage doublers are cascaded to form a complete harvester, with configurable overall conversion ratio from 9× to 23×. In each voltage doubler, the oscillator is completely internalized within the SC network, eliminating clock generation and level shifting power overheads. A single doubler has >70% measured efficiency across 1 nA to 0.35 mA output current ( >10 5 range) with low idle power consumption of 170 pW. In the harvester, each doubler has independent frequency modulation to maintain its optimum conversion efficiency, enabling optimization of harvester overall conversion efficiency. A leakage-based delay element provides energy-efficient frequency control over a wide range, enabling low idle power consumption and a wide load range with optimum conversion efficiency. The harvester delivers 5 nW-5 μW output power with >40% efficiency and has an idle power consumption 3 nW, in test chip fabricated in 0.18 μm CMOS technology.
Indoor photovoltaic energy harvesting is a promising candidate to power millimeter (mm)-scale systems. The theoretical efficiency and electrical performance of photovoltaics under typical indoor ...lighting conditions are analyzed. Commercial crystalline Si and fabricated GaAs and Al 0.2 Ga 0.8 As photovoltaic cells were experimentally measured under simulated AM 1.5 solar irradiation and indoor illumination conditions using a white phosphor light-emitting diode to study the effects of input spectra and illuminance on performance. The Al 0.2 Ga 0.8 As cells demonstrated the highest performance with a power conversion efficiency of 21%, with open-circuit voltages >0.65 V under low lighting conditions. The GaAs and Al 0.2 Ga 0.8 As cells each provide a power density of ~100 nW/mm 2 or more at 250 lx, sufficient for the perpetual operation of present-day low-power mm-scale wireless sensor nodes.
Circuit blocks for a 1.5 mm 3 microsystem enable continuous monitoring of intraocular pressure. Due to power and form-factor limitations, circuit blocks are designed at nanowatt power levels not ...completely explored before. The system includes a 75% efficient 90 nW DC-DC converter which is the most efficient reported sub- μW converter in literature. It also includes a novel 4.7 nJ/bit FSK radio that achieves 10 cm of transmission range at 10 -6 BER which is also the lowest number reported for short-range through-tissue wireless links for biomedical implants. A MEMS capacitive sensor and ΣΔ capacitance-to-digital converter measure IOP with 0.5 mmHg accuracy. A microcontroller processes and saves IOP data and stores it in a 2.4 fW/bitcell SRAM. The microsystem harvests a maximum power of 80 nW in sunlight with a light irradiance of 100 mW/cm 2 AM 1.5 from an integrated 0.07 mm 2 solar cell to recharge a 1 mm 2 1 μAh thin-film battery and power the load circuits. The design achieves zero-net-energy operation with 1.5 hours of sunlight or 10 hours of bright indoor lighting daily.
This paper, split into Parts I and II, reviews recent innovations in circuit design that have accelerated the miniaturization of sensor nodes. Design techniques for key building blocks, such as ...sensor interfaces, timing reference, data communication, energy harvesting, and power management are reviewed. In particular, Part I introduces analog circuit techniques and sensor interfaces for miniaturized sensor nodes. The energy budget of such system is highly restricted due to the small battery volume. Therefore, ultra-low power design techniques are critical enablers and are reviewed. Design techniques for compact monolithic integration are also discussed.
This two-part paper reviews recent innovations in circuit design that have accelerated the miniaturization of sensor nodes. In this second part of the paper, we focus on key building blocks of ...miniaturized sensor nodes, such as data transceivers, energy harvesters, power management units, and digital logic circuits. System level design considerations are also discussed to provide guidelines for the design of a miniaturized system. As an example prototype design, a 2.7-cm 3 global navigation satellite system (GNSS) logger is proposed. This paper includes a die-stacked sensor platform composed of an ARM cortex M0 processor, energy harvester, power management unit, solar cell, optical receiver, sensor layer, and RF transmitter that exploits the discussed design techniques for ultra-low power operation. The GNSS logger can store GNSS signals of >1 k positions on a single battery charging without additional energy harvesting.
A self-sustainable sensing platform powered entirely by small-scale benthic microbial fuel cells (MFCs) for oceanic sensing applications is presented. An ultra-low power chip featuring an ARM ...Cortex-M0 processor, 3 kB of SRAM, and power management unit (PMU) is designed to consume 11 nW in sleep mode for perpetual sensing operation. The PMU includes a switched-capacitor DC/DC converter designed for efficient energy harvesting and step-down conversion for a wide range of input and output power. A small-scale MFC with 21.3 cm 2 anode surface area was connected to the PMU to charge a thin-film battery of 1 mAh capacity. A 49.3-hour long-term experiment with 8-min sleep interval and 1-s wake-up time demonstrated the sustainability of system-on-mud concept. During sleep mode operation, the system charges the 4 V battery at 380 nA from the micro-MFC generating 5.4 μW of power, which allows up to 20 mA of active mode current with net energy neutrality.
This paper describes two platforms for autonomous sensing microsystems that are intended for deployment in chemically corrosive environments at elevated temperatures and pressures. Following the ...deployment period, the microsystems are retrieved, recharged, and interrogated wirelessly at close proximity. The first platform is the Michigan Micro Mote for High Temperature (M³HT), a chip stack 2.9 × 1.1 × 1.5 mm³ in size. It uses RF communications to support pre-deployment and post-retrieval functions, and it uses customized electronics to achieve ultralow power consumption, permitting the use of a chip-scale battery. The second platform is the Environmental Logging Microsystem (ELM). This system, which is 6.5 × 6.3 × 4.5 mm³ in size, uses the smallest suitable off-the-shelf electronic and battery components that are compatible with assembly on a flexible printed circuit board. Data are stored in non-volatile memory, permitting retrieval even after total power loss. Pre-deployment and post-retrieval functions are supported by optical communication. Two types of encapsulation methods are used to withstand high pressure and corrosive environments: an epoxy filled volume is used for the M³HT, and a hollow stainless-steel shell with a sapphire lid is used for both the M³HT and ELM. The encapsulated systems were successfully tested at temperature and pressure reaching 150 °C and 10,000 psi, in environments of concentrated brine, oil, and cement slurry. At elevated temperatures, the limited lifetimes of available batteries constrain the active deployment period to several hours.
Glaucoma is the leading cause of blindness, affecting 67 million people worldwide. The disease damages the optic nerve due to elevated intraocular pressure (IOP) and can cause complete vision loss if ...untreated. IOP is commonly assessed using a single tonometric measurement, which provides a limited view since IOP fluctuates with circadian rhythms and physical activity. Continuous measurement can be achieved with an implanted monitor to improve treatment regiments, assess patient compliance to medication schedules, and prevent unnecessary vision loss. The most suitable implantation location is the anterior chamber of the eye, which is surgically accessible and out of the field of vision. The desired IOP monitor (IOPM) volume is limited to 1.5mm 3 (0.5x1.5x2mm 3 ) by the size of a self-healing incision, curvature of the cornea, and dilation of the pupil.
We present a near-field radio system for a millimeter-scale wireless smart sensor node that is implantable through a 14-gauge syringe needle. The proposed system integrates a radio system on chip and ...a magnetic antenna on a glass substrate within a total dimension of 1 × 1 × 10 mm 3 . We demonstrate energy-efficient active near-field wireless communication between the millimeter-scale sensor node and a base station device through an RF energy-absorbing tissue. The wireless transceiver, digital baseband controller, wakeup controller, on-chip baseband timer, sleep timer, and MBUS controller are all integrated on the SoC to form a millimeter-scale sensor node, together with a 1 × 8 mm 2 magnetic antenna fabricated with a 1.5-μm-thickness gold on a 100 μm-thickness glass substrate. An asymmetric link is established pairing the sensor antenna with a codesigned 11 × 11 cm 2 base station antenna to achieve a link distance of up to 50 cm for sensor transmission and 20 cm for sensor reception. The transmitter consumes a 43.5 μW average power at 2 kb/s, while the receiver power consumption is 36 μW with a -54 dBm sensitivity at 100 kb/s. When powered by a 1×2.2 mm 2 thin-film battery (2 μAh, 4.1 V), the designed system has a two week expected lifetime without battery recharging when the system wakes up and transmits and receives 16 b data every 10 min.
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