정완영 교수

The response of wall-flow turbulence to high-frequency spanwise oscillations was investigated by direct numerical simulations of a planar channel flow subjected either to an oscillatory spanwise cross-flow or to the spanwise oscillatory motion of a channel wall. Periods of oscillation, Tosc+=Toscuτ2/ν, ranging from 25 to 500 were studied. For 25≤Tosc+≤200 the turbulent bursting process was suppressed, leading to sustained reductions of 10% to 40% in the turbulent drag and comparable attenuations

The Internet of Things (IoT) is a rapidly emerging application space, poised to become the largest electronics market for the semiconductor industry. IoT devices are focused on sensing and actuating of our physical environment and have a nearly unlimited breadth of uses. In this paper, we explore the IoT application space and then identify two common challenges that exist across this space: ultra-low power operation and system design using modular, composable components. We survey recent low pow

This paper presents a fully integrated energy harvester that maintains >35% end-to-end efficiency when harvesting from a 0.84 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> 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× t

Thermal sensing is one of the most commonly desired features in IoT devices to monitor either environmental or system/chip conditions. An accurate temperature sensor usually requires carefully calibrated, high-accuracy ADCs, which prevents their use in ultra-low-power sensor nodes. In some sensing architectures, a highly accurate timing reference can replace the ADC [1]. With this in mind, we observe that almost all IoT systems incorporate a high-accuracy timing source (real-time clock, RTC) for

Near-threshold computing (NTC) is an attractive solution to stagnating energy efficiencies in digital integrated circuits, arising from slowed voltage scaling in nanometer CMOS [1-2]. The design of sequential elements for NTC, as well as in voltage-scaled systems operating at both near-threshold and super-threshold, has not been extensively studied. However, it is well known that sequential elements have a strong sensitivity to process variations in NTC [2], which can have a significant impact o

Recent advances in low-power circuits have enabled mm-scale wireless systems [1] for wireless sensor networks and implantable devices, among other applications. Energy harvesting is an attractive way to power such systems due to limited energy capacity of batteries at these form factors. However, the same size limitation restricts the amount of harvested power, which can be as low as 10s of nW for mm-scale photovoltaic cells in indoor conditions. Efficient DC-DC up-conversion at such low power l

A dual-slope capacitance-to-digital converter for pressure-sensing is presented and demonstrated in a complete microsystem. The design uses base capacitance subtraction with a configurable capacitor bank to narrow down input capacitance range and reduce conversion time. An energy-efficient iterative charge subtraction method is proposed, employing a current mirror that leverages the 3.6 V battery supply available in the system. We also propose dual-precision comparators to reduce comparator powe

Capacitance sensors are widely used to measure various physical quantities, including position, pressure, and concentration of certain chemicals [1-6]. Integrating capacitive sensors into a small wireless sensor system is challenging due to their large power consumption relative to the total system power/energy budget, which can be as low as a few nW [4]. Typical capacitance-to-digital converters (CDCs) use charge sharing or charge transfer between capacitors to convert the sampled capacitance t

This paper presents a new energy-efficient ring oscillator collapse-based comparator, named edge-pursuit comparator (EPC). This comparator automatically adjusts the performance by changing the comparison energy according to its input difference without any control, eliminating unnecessary energy spent on coarse comparisons. Furthermore, a detailed analysis of the EPC in the phase domain shows improved energy efficiency over conventional comparators even without energy scaling, and wider resoluti

An incremental zoom-in capacitance-to-digital converter (CDC) is proposed. By using a 9b SAR, the OSR can be reduced to only 32, significantly improving conversion energy. We show how the OTA in the SAR is bypassed for the CDC further reducing energy and propose a novel matrix based 512-element unit-cap structure for dynamic element matching. The CDC achieves 94.7dB SNR and 33.7µW power consumption with 175fJ/conv-step at 1.4V supply.

As Internet-of-Things (IoT) systems proliferate, there is a greater demand for small and efficient power management units. Fully integrated switched-capacitor (SC) DC-DC converters are promising candidates due to their small form factor and low quiescent power, aided by dynamic activity scaling [1-3]. However, they offer a limited number of conversion ratios, making them challenging to use in actual systems since they often require multiple output voltages (to reduce power consumption) and use v

Switched-capacitor (SC) DC-DC converters have several advantages over inductive DC-DC converters in that they are easily integrated on-chip and can scale to desired power levels, rendering themselves promising for integrated voltage regulators, especially for small, low-power systems. However, many SC DC-DC converters offer only a few conversion ratios, limiting their use for systems in which either the input or output voltages vary. This is particularly important in wireless systems where batte