Donghwa Shin

• Professor (Assistant) at Yeungnam University

The variability in manufacturing process and operating conditions has a significant impact on the operation of memristor devices, since it is usually implemented in nano-scale for higher density. The variability in thickness and area can be regarded as a source of variations in read and write times of memristor when using the device as a memory cel...

The reliability and efficiency of a physically unclonable function (PUF) considerably depends on that of the random seed number generation process in the target hardware technology. Among the proposed hardware PUF techniques, flash memory-based approaches have several advantages because of the widespread use of flash memories in electronic devices....

The dependence between the write time and process variation of a memristor was investigated as a candidate physically unclonable function (PUF). Such write-time-based approach requires exact timing control of the programming pulse to achieve well-balanced results as the source of randomness. However, exact timing control requires precise hardware,...

AC power adapters for battery-operated systems, such as smartphones and notebook computers, not only supply run-time power to operate the devices but also charge the built-in batteries. The capacity of the adapter is optimized for the average power demand rather than the maximum power demand to reduce the size and weight of the adapter. Such a redu...

Conventional internal combustion engine vehicles generally have less than a 30% of fuel efficiency, and the most wasted energy is dissipated in the form of heat energy. The excessive heat dissipation is a primary reason of poor fuel efficiency, but reclamation of the heat energy has not been a main focus of vehicle design. Thanks to thermoelectric...

Thermal analysis and management of batteries have been an important research issue for battery-operated systems, such as electric vehicles and mobile devices. Nowadays, battery packs are designed considering heat dissipation, and external cooling devices, such as a cooling fan, are also widely used to enforce the reliability and extend the lifetime...

Power cells, such as battery cells, solar cells, and fuel cells, are often connected in series and parallel to satisfy a desired amount of power and energy density as well as the terminal voltage. However, it is allowed to compose an array of power cells only when the individual cell has the identical characteristics among each other. However, even...

A framebuffer memory is data storage for the displayed image, which is one of the major power consumers in display systems. This paper proposes a power reduction technique for the on-chip framebuffer cache (FBC) performing a compressed image data management. The proposed architecture stores the compressed image data in the on-chip FBC, and the disp...

Modern embedded systems are typically operated by the rechargeable batteries in our daily life. Since charge of batteries is considered as an time consuming task, there have been extensive efforts to manage the charge time from the perspective of materials, circuits, and systems. Estimation of battery charge time is one of the essential information...

With the remarkable recent rise in the production of battery-powered devices, their reliability analysis cannot disregard the assessment of battery life. In the literature, there are several battery cycle life models that exhibit a generic trade-off between generality and accuracy. In this work we propose a compact cycle life model for batteries of...

Large liquid crystal display (LCD) technology is being widely used in every corner of our modern life, ranging from personal laptops to flat-panel televisions. Among all the components in an LCD display system, the backlight panel is the dominant power consumer, irrespective of lighting technology or class. In this paper, a saliency-based field-pro...

Non-volatile counter is a counter that maintains the value without external power supply. It has been used for the applications related to warranty issues to count and record certain events such as power cycles, operating time, hard resets, and timeouts. It has been conventionally implemented with volatile memory-based counter and battery backup or...

Fuel cells generally have a higher energy density by a lower power density than batteries, and a fluctuating load can cause unstable operation as well as low efficiency. A hybrid in which a fuel cell is combined with an energy storage element with higher power density, such as a battery or supercapacitor, can enhance the load-following capability o...

The evaluation of the cycle life of batteries is an essential task in the assessment of the reliability and cost of battery-operated devices. Several compact cycle life models have been proposed in the literature, that exhibit a general trade-off between generality and accuracy. Some models are based on a compact equation derived from experimental...

LPDDR2-NVM has been announced as an industry standard to efficiently interface with non-volatile memory devices such as phase change memory (PCM). This standard interface has been adopted in most commercial PCM devices. In this paper, we devise a prefetch-based dynamic row buffer management that targets the LPDDR2-NVM devices for enhancing performa...

Phase change memory (PCM) is an attractive candidate for the future memory, but it still has several limitations to overcome such as write latency and long-term endurance. A large body of literature has been dedicated to solving these problems. However, almost all of the previous studies did not consider an important practical aspect of the PCM - a...

The cell-to-cell variability of batteries is a well-known problem particularly when it comes to the assembly of large battery packs. Different battery cells exhibit substantial variability due to manufacturing tolerances, which should be assessed and managed carefully. Such variability has been approached mostly from the point of view of the chemic...

This paper introduces a joint charge and thermal management problem for batteries in a battery-supercapacitor hybrid power source of a portable system, which has been equipped with a forced convection cooling technique, such as a fan. A key consideration in such a system is that the battery aging depends strongly on the battery temperature, which i...

Low power double data rate 2 non-volatile memory (LPDDR2-NVM) has been deemed the standard interface to connect non-volatile memory devices such as phase-change memory (PCM) directly to the main memory bus. However, most of the previous literature does not consider or overlook this standard interface. In this paper, we propose address phase skippin...

The de-facto standard approach in battery modeling consists of the definition of a generic model template in terms of an equivalent electric circuit, which is then populated either using data obtained from direct measurements on actual devices or by some extrapolation of battery characteristics available from datasheets. These models typically desc...

Availability of a simulation model of a battery is one of the most important requisites in the system-level design of battery-powered systems. The vast majority of the models describe the discharge behavior of the battery; so far, the estimation of charging time has been in fact only marginally studied because the charging phase is regarded as a re...

The market of portable devices, wireless sensors, electric vehicles and storage systems has grown enormously in recent years. As a consequence, batteries and related technologies have become one of the major topics for researchers. Due to the large variety of applications in which batteries are involved, battery modeling is becoming an extremely im...

Smartphones consume a significant amount of power. Indeed, they can hardly provide a full day of use between charging operations even with a 2000 mAh battery. While power minimization and dynamic power management techniques have been heavily explored to improve the power efficiency of modules (processors, memory, display, GPS, etc.) inside a smartp...

This paper introduces a novel sensor-less, event-driven power analysis framework called FEPMA for providing highly accurate and nearly instantaneous estimates of power dissipation in an Android smartphone. The key idea is to collect and correctly record various events of interest within a smartphone as applications are running on the application pr...

Thermal analysis and management of batteries have been an important research issue for battery-operated systems such as electric vehicles and mobile devices. Nowadays, battery packs are designed considering heat dissipation, and external cooling devices such as a cooling fan are also widely used to enforce the reliability and extend the lifetime of...

Electrical energy systems (EESs) include energy generation, distribution, storage, and consumption, and involve many diverse components and sub-systems to implement these tasks. This paper represents a first step towards the computer-aided design for EESs, encompassing modeling, simulation, design and optimization of these systems. CAD for EESs is...

The thermal management is a crucial design problem for mobile devices because it greatly affects not only the device reliability, but also the leakage energy consumption. Conventional dynamic thermal management (DTM) techniques work well for the computer systems. However, due to the limitation of the physical space in mobile devices, the thermal co...

Models based on an electrical circuit equivalent have become the most popular choice for modeling the behavior of batteries, thanks to their ease of co-simulation with other parts of a digital system. Such circuit models are actually model templates: the specific values of their electrical elements must be derived by the analysis of the specific ba...

Many solutions for battery modeling have been proposed in the literature; they usually rely on the definition of a generic model template (e.g., a circuit equivalent), which is then populated using data obtained from direct measurements on actual devices. This approach incurs in high costs (for the instrumentation) and long characterization times....

Due to manufacturing tolerances, different battery cells exhibit substantial variability among them, which should be carefully assessed and managed, especially when assembling large battery packs. Cell-to-cell variability has been mostly approached from the point of view of the chemical and physical phenomena, but these studies did not provide a pr...

Organic light emitting diode (OLED) display is a self-illuminating device that is supposed to be more power efficient than liquid crystal display (LCD). However, OLED display panels consume as much power as LCD panels due to total internal reflection. As the power consumption of the OLED panel depends on the pixel colors, most of the earlier power...

Dynamic voltage and frequency scaling (DVFS) has been studied for well over a decade. Nevertheless, existing DVFS transition overhead models suffer from significant inaccuracies; for example, by incorrectly accounting for the effect of DC-DC converters, frequency synthesizers, voltage, and frequency change policies on energy losses incurred during...

Cycle life of a battery largely varies according to the battery operating conditions, especially the battery temperature. In particular, batteries age much faster at high temperature. Extensive experiments have shown that the battery temperature varies dramatically during continuous charge or discharge process. This paper introduces a forced convec...

In this paper, a bio-inspired technique of finding the regions of highest visual importance within an image is proposed for reducing power consumption in modern liquid crystal displays (LCDs) that utilize a 2D light-emitting diode (LED) backlighting system. The conspicuity map generated from this neuromorphic saliency model, along with an adaptive...

Emerging mobile systems integrate a lot of functionality into a small form factor with a small energy source in the form of rechargeable battery. This situation necessitates accurate estimation of the remaining energy in the battery such that user applications can be judicious on how they consume this scarce and precious resource. This paper thus f...

A joint optimization of the physical system and the cyber world is one of the key problems in the design of a cyber-physical system (CPS). The major mechanical forces and/or chemical reactions in a plant are commonly modified by actuators in the balance-of-plant (BOP) system. More powerful actuators requires more power, but generally increase the r...

A modern smartphone or tablet-PC is typically equipped a high-resolution and large-size display, which is a primary power consumer. In spite of the relatively high power efficiency of organic light emitting diode (OLED) displays, the integrated display subsystem exhibits low energy efficiency due to power losses in the battery and the boost voltage...

Modern smartphones consume significant power and can hardly provide a full day's use between charging operations even with a 2000 mAh battery. This is in spite of many power management techniques being employed in the smartphones. This paper starts from the observation that modern smartphones waste a significant amount of the battery's stored energ...

Partial shading is a serious obstacle to effective utilization of photovoltaic (PV) systems since it can result in significant output power degradation for the system. A PV system is organized as a series connection of PV modules, each module comprising of a number of series-parallel connected cells. This paper presents modified PV cell structures...

Modern batteries provide high discharging efficiency, but the rate capacity effect in these batteries drastically decreases the discharging efficiency as the load current increases. Electric double layer capacitors, or simply supercapacitors, have extremely low internal resistance, and a battery-supercapacitor hybrid may mitigate the rate capacity...

This paper is the first to present an efficient charge management algorithm focusing on extending the cycle life of battery elements in hybrid electrical energy storage (HEES) systems while simultaneously improving the overall cycle efficiency. In particular, it proposes to apply a crossover filter to the power source and load profiles. The goal of...

Hybrid electrical energy storage (HEES) systems are composed of multiple banks of heterogeneous electrical en-ergy storage (EES) elements with distinctive properties. Charge replacement in a HEES system (i.e., dynamic assignment of load demands to EES banks) is one of the key operations in the sys-tem. This paper formally describes the global charg...

Unlike liquid crystal display (LCD) panels that require high-intensity backlight, organic LED (OLED) display panels naturally consume low power and provide high image quality thanks to their self-illuminating characteristic. In spite of this fact, the OLED display panel is still the dominant power consumer in battery-operated devices. As a result,...

Modern batteries (e.g., Li-ion batteries) provide high discharge efficiency, but the rate capacity effect in these batteries drastically decreases the discharge efficiency as the load current increases. Electric double layer capacitors, or simply supercapacitors, have extremely low internal resistance, and a battery-supercapacitor hybrid may mitiga...

Conventional dynamic thermal management (DTM) assumes that the thermal resistance of a heat-sink is a given constant determined at design time. However, the thermal resistance of a common forced-convection heat sink is inversely proportional to the flow rate of the air or coolant at the expense of the cooling power consumption. The die temperature...

This paper introduces a complete system-level design and integration of a portable direct methanol fuel cell (DMFC) system. We describe hardware and software design for the balance of plant (BOP) control, including a 32-bit microprocessor and electronics for actuators and sensors, focusing on reliable operation and protection of the DMFC system. Va...

Modern vehicle electronics control units (ECUs) are getting rapidly complicated because of active safety and semi-autonomous driving controls, such as electric stability program (ESP) and adaptive cruise control (ACC). Furthermore, the operational environment of ECUs is extremely harsh, especially in terms of an ambient temperature well exceeding 1...

Dynamic voltage and frequency scaling (DVS) has been studied for well over a decade, and even commercial systems widely support DVS nowadays. Nevertheless, existing DVS transition overhead models do not accurately reflect modern DVS architectures including modern DC-DC converters, PLL (Phase Lock Loop), and voltage and frequency change policies. In...

Direct methanol fuel cells (DMFCs) are a promising nextgeneration energy source for portable applications, due to their high energy density and the ease of handling of the liquid fuel. However, the limited range of output power obtainable from a fuel cell requires hybridization the introduction of a battery to form a stand-alone portable power sour...

Existing thermal management systems for microprocessors assume that the thermal resistance of the heat-sink is constant and that the objective of the cooling system is simply to avoid thermal emergencies. But in fact the thermal resistance of the usual forced-convection heat-sink is inversely proportional to the fan speed, and a more rational objec...

Memory devices often consume more energy than microprocessors in current portable embedded systems, but their energy consumption changes significantly with the type of transaction, data values, and access timing, as well as depending on the total number of transactions. These variabilities mean that an innovative tool and framework are required to...

We discover significant value-dependent programming energy variations in multi-level cell (MLC) flash memories, and introduce an energy-aware data compression method that minimizes the flash programming energy rather than the size of the compressed data. We express energy-aware data compression as an entropy coding with unequal bit-pattern costs. D...