Zero Standby Power Remote Control System using Light ... - IEEE Xplore

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IEEE Transactions on Consumer Electronics, Vol. 57, No. 4, November 2011

Zero Standby Power Remote Control System using Light Power Transmission Sungmuk Kang, Kyungjin Park, Seunghwan Shin, Keunsu Chang, and Hoseong Kim Abstract — All commercial remotely controllable home appliances consume electric power while in standby mode waiting for a remote signal. This paper presents a new remote control system that consumes absolute zero power in standby mode. In this system, the home appliance is physically disconnected from the AC power line by a latch-type power relay in standby mode. When a laser beam is emitted from a remote controller to turn on the home appliance, the photovoltaic array mounted on the home appliance receives and accumulates the light energy in a storage capacitor. An autonomous connection circuit is devised and used to separate the storage capacitor from the power relay to prevent discharge during the light energy accumulation stage. When the proposed remote control system is implemented on a 190 W commercial television, use of a 15 mW infrared (830 nm) laser light for 620 ms turns it on at a distance of 2 m in a completely dark room. It can then be turned off using commercial remote controller1. Index Terms —Home Appliances, Zero Standby Power, Light Energy Transmission, Remote Control.

I. INTRODUCTION Environmental and energy conservation continue to attract more and more attention. In particular, growing awareness of and concerns about environmental issues have been caused by increases in the use of fossil fuels such as coal, oil, and natural gas. Based on this awareness, policies that categorize highly energy-efficient appliances into environmentally friendly groups and encourage consumers to buy them are enforced in many countries. One of the largest energy-saving efforts involves reducing standby power in consumer electronics. Standby power is the power consumed by a product when it is switched off or is not performing its primary purpose [1]. All home appliances continuously consume electric power while waiting for a remote signal; in fact, surveys show that total standby energy is about 10 % of the electricity used in a home [1]-[2]. 1

This research was supported by the Chung-Ang University Research Scholarship Grant in 2009 and by grants from Samsung Electronics Co. Ltd. (2010). Sungmuk Kang is with School of Electrical and Electronics Engineering, Chung-Ang University, Seoul, Korea (e-mail: [email protected]). Kyungjin Park is with School of Electrical and Electronics Engineering, Chung-Ang University, Seoul, Korea (e-mail: [email protected]). Seonghwan Shin is with School of Electrical and Electronics Engineering, Chung-Ang University, Seoul, Korea (e-mail: [email protected]). Keunsu Chang is with School of Electrical and Electronics Engineering, Chung-Ang University, Seoul, Korea (e-mail: [email protected]). Hoseong Kim is with School of Electrical and Electronics Engineering, Chung-Ang University, Seoul, Korea (e-mail: [email protected]). Contributed Paper Manuscript received 10/11/11 Current version published 12/27/11 Electronic version published 12/27/11.

Among standby functions such as memorizing the previous state, time display, and remote control, the remote control is essential for convenience, while the DC power consumption for this function is very low, only a few tens of milliwatts [3]. Since power supplies such as switching mode power supply (SMPS) and linear power supply show poor efficiency at the low power level [4], appliances consume power many times higher than that actually used. Unplugging devices is the simplest way to solve the problem, but it presents a hassle. Recently published papers have shown that various attempts have been made to improve power supply conversion efficiency through varying the duty ratio of transformer according to appliances’ instantaneous power consumption [5]-[8]. Absolute zero standby power studies are just starting be published [9]-[10]. Absolute zero standby power technology using RFID technology was introduced in 2010; however, a large directional antenna was required on the remote controller and a battery was required to drive a relay [9]. Tsai et al proposed the use of a power socket with photovoltaic (PV) cells for ambient light energy harvesting and a PIR sensor to detect the user’s approach of the socket [10]. However, in a dark room, the socket has to consume standby power from the AC power line and may unintentionally connect appliances to the AC power line every time the user approaches it. In this paper, we propose a new light-powered remote control system to achieve absolute zero standby power for home appliances. In our system, a 15 mW laser diode is mounted on a commercial remote controller. A 2 cm  2.5 cm PV array, an autonomous connection circuit (ACC), and latchtype power relay are mounted on a receiver unit that does not have any other power source. This dead receiver that does not have any power source receives light energy, revives from death, and connects the home appliance to the AC power line once the stored energy is high enough to drive the relay. The home appliance is turned off in the usual way using a commercial remote controller, but the receiver unit latches off the relay to physically disconnect the appliance from the AC power line. The proposed system was designed for and implemented on a commercial LCD television (TV). This paper is organized as follows. The proposed system architecture is presented in section II. The optical system design and autonomous connection circuit design are presented in section III. The experiment results are reported in section IV, while the conclusions are discussed in section V. II. PROPOSED ARCHITECTURE The easiest and most tangible way to achieve absolute zero standby power is to unplug or manually switch off an

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S. Kang et al.: Zero Standby Power Remote Control System using Light Power Transmission

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appliance, but this solution is cumbersome and not very effective due to human laziness. To overcome this problem and achieve absolute zero standby power, we have designed and herein present a new light-powered remote control system. The main idea of this proposed system is conceptually shown in Figure 1.

Fig. 2. Block diagram of the zero standby power remote control system for high power application with the function of identification.

Fig. 1. Block diagram of the zero standby power remote control system.

The home appliance is initially disconnected from the AC power line by the latch relay to consume absolute zero power. Whenever a laser beam impinges upon the PV array to turn on the appliance, the PV array converts the photon energy to electric power and accumulates it in a storage capacitor. In order to prevent energy leakage during this energy accumulation stage, the latch relay is separated from the storage capacitor by the ACC until sufficient energy is accumulated in the storage capacitor. When the amount of accumulated energy is sufficient to drive the latch relay, the ACC autonomously connects the storage capacitor to the control port of the latch relay, and the relay connects the home appliance to the AC power line. The operating appliance can be turned off using a commercial remote controller as conventional way, but in our system, the receiver unit latches off the relay to physically disconnect the appliance from the AC power line and return it to standby mode consuming absolute zero power. As explained above, a dead receiver receives the light energy, revives from death and connects the appliance to AC power. The remote control system shown in Fig. 1 can be directly applied to low-power (a few tens of watts) home appliances such as small TVs, computer monitors, and audio equipment. However the high-capacity power relays mounted on higher power appliances require too much power to be activated by light power transmission. Furthermore, the system shown in Fig. 1 is susceptible to light noises such as sunlight, lightning, fluorescent light, and other infrared (IR) commanding lights of adjacent appliances. Thus, an advanced system that can be applied to high-power home appliances that has an identification (ID) function is proposed here. The architecture of the advanced system is shown in Figure 2. Unlike the system in Fig. 1, a small capacity auxiliary latch relay and a small capacity AC/DC converter are utilized to supply power for an ID check unit. As with the system shown in Fig. 1, the home appliance is disconnected from the AC power line by a main latch relay, making it consume absolute zero power.

When ON button is pressed on the remote controller, a 15 mW, 830 nm laser diode (LD) mounted on the remote controller continuously transmits a laser beam for 1 s followed by the coded ID and ON command signals as shown in Fig. 2. The coded ID and ON command signals are transmitted from the IR light-emitting diode (LED) of the remote controller. Using laser beam energy, the ACC sets the auxiliary relay and then the auxiliary AC/DC converter supplies power to the ID check unit, which checks whether the received ID and command signal match the appliance’s ID and command. If they match, the microcontroller unit (MCU) in the ID check unit sends a pulse to set the main relay, the main AC/DC converter is activated, and the appliance turns on. After that, the auxiliary AC/DC converter and ID check unit remain live and wait for another command from the conventional remote controller. If coded ID and ON command signal do not match, the MCU sends a pulse to reset the auxiliary latch relay as shown in Fig. 2. In this situation, the main latch relay stays in a cut-off state in which it consumes absolute zero standby power. In our experiment, the ID check unit that is embedded in the appliance is taken out from the appliance and modified to include the latch relay controller. The nominal operating power of the main relay is about 10 times higher than that of the auxiliary relay. When the OFF command is received by the ID check unit while the appliance is working, the receiver unit sends two pulses, one to reset the main relay to cut off the appliance and the other to reset the auxiliary relay to cut off the receiver itself returning to an absolute zero power standby mode. By the way, since the LD works for 1 s, usually a few times a day only if the ON button is pressed, the decline in the battery life time of the remote controller is considered insignificant. The ACC and the optical system, the most important parts of this system, are described in following sections. III. SYSTEM DESIGN A. ACC Design To accumulate incoming energy in a storage device and use it at once without any external intervention, an elaborate device is required that can monitor energy level, make a

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decision and connect the load. It is natural that power is required to perform these functions. However, in our system, the only available power source is the accumulated energy in the storage capacitor. Furthermore, the extracted electrical energy from the light of the LD is very low, in the order of microwatts and the voltage across the storage capacitor is not constant, since it increases from 0 volts. Therefore, a switching circuit that can monitor the energy level with extremely low power leakage and autonomously connect the load when the accumulated energy is sufficiently high to drive the load is needed. Figure 3 is a schematic of the ACC connected to the auxiliary latch relay as a load. The ACC is adapted from a similar circuit designed for energy harvesting [11]-[12] and has been revised to reflect the very low impedance of the latch relay.

Fig. 3. Schematic of the autonomous connection circuit.

This circuit works as follows. Q1, Q2, and Q3 are initially off, meaning that the ground is floating due to the off state of Q2 and Q3, and the latch relay is unpowered. Since there is no discharge path for the storage capacitor Cs, charges generated by the photovoltaic array are accumulated on the storage capacitor Cs. The leakage in this accumulation stage consists of an emitter-collector leakage current of Q1 and a leakage current of the zener diode D1. As the storage capacitor voltage increases to values comparable to the zener voltage, the leakage currents also increase and induce low voltage on the Q2 gate. This low gate voltage and a large resistance R3 force on Q2 operate in the sub-threshold region. Since the subthreshold current in the order of pA is much smaller than the photo-generated current, the storage capacitor voltage keeps increasing. When the storage capacitor voltage increases to VACC (i.e., the zener voltage plus the base-emitter voltage drop of Q1), Q1 turns on and the emitter-collector current abruptly starts to increase. The current increase subsequently increases the gate voltage of Q2, resulting in its activation. Voltage across R3 then increases, and Q3 gate voltage increases and activates Q3. This connects the ground line to the complete discharge loop of the storage capacitor through the latch relay coil, and a large current then flows through the relay coil to latch the relay. As soon as the large discharge current flows through the relay coil, the Cs voltage drops sharply below the threshold gate voltages of Q2 and Q3, deactivating them and floating the ground. If the relay was directly connected to Q2 without Q3, the storage capacitor voltage would never reach to the VACC since the relatively large discharge current flows

through the low impedance of the relay coil. Finally, R4 and D2 were included to protect FETs from counter-electromotive forces in the relay coil and further incoming laser beam will increase the storage capacitor voltage. Figure 4 shows the voltage (upper trace) of 10 μF Cs and the output voltage (lower trace) of the auxiliary AC/DC converter shown in Fig. 2. When the laser beam illuminates the PV array in a dark room, the capacitor voltage is raised from zero (Fig. 4(a)). After 620 ms, when the voltage of the storage capacitor reaches to 5.6 V, the storage capacitor starts discharge and the latch relay is set. As mentioned above, since the laser turn-on time is set to 1 s, the voltage of the storage capacitor increases again after discharging.

(a) (b) Fig. 4. The waveform of the voltage on the storage capacitor (upper trace) and the supply auxiliary AC/DC converter output (lower trace); (a) in the dark, and (b) at 300 lx indoor illumination.

Fig. 4(b) shows the waveforms when the laser beam illuminates the PV array in a bright room with 300 lx illumination. Although the room light is not sufficient to operate the ACC, the capacitor voltage is raised from 1.4 V due to the ambient light. It is found that the ACC turns on twice in 1 s of laser illumination but that there is no change in the auxiliary AC/DC converter output. Since the indoor home or office illumination is generally about 300 lx, the actual situation is closer to that in Fig. 4(b) than that in Fig. 4(a). B. Optical System Design The optical system has a major effect on our system’s delay time. The amount of time, T, required to turn on the ACC with the light power can be expressed as follows:

T

Q C S  V ACC  i i ph  id

(1)

where Cs is the capacitance of the storage capacitor, VACC is the threshold operation voltage of the ACC, iph and id are the photocurrent and the diffusion current, respectively, of the PV cell. The photocurrent iph can be expressed as follows:

i ph  

Pop Ae h

(2)

where η is the external quantum efficiency (EQE) of the PV cell, Pop is the optical power density [W/ cm2], A is the photovoltaic cell area [cm2], e is the electronic charge, h is the


Planck’s constant and ν is the light frequency. Using (2), (1) can be rewritten as: T

C S  VACC P Ae  op  id h

(3)

In our system, Cs is 10 uF, VACC is 5.6 V, and Pop is determined by the light source characteristic. η, A and id are determined by the PV cell characteristics. The goals of optical design are to maximize the operation distance and minimize the laser on time. The design parameters are determined as described below. An LD with a 15 mW total output light power and an 830 nm wavelength was used for light power transmitter. The total output light power of an LED mounted to a commercial remote controller is 50 mW. Although the total output light power of the LD is much lower than that of the LED, the LD intensity is much higher. Therefore, the LD was chosen to maximize the energy transfer efficiency and working distance of our remote control system. Since the LD beam size was too small to cover the PV array area, a lens was inserted to expand the beam size. The half divergence angles were measured horizontally at 4.5 mrad and vertically at 7.5 mrad at 50 % beam truncation. Assuming uniform illumination within the divergence angle, the average intensity Pop at the distance of d can be estimated as follows: Pop 

0.5  15 mW

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Figure 5(a). The area A in (3), the area of a single cell, is 0.28 cm2 (Figure 5(a)). The measured EQE, including the reflection effect, is about 0.3. A total of 7 GaAs PV cells are used and elliptically positioned (Figure 5(b)) to match the beam shape. The 7 cells are connected in a series to obtain higher output voltage than the VACC which is 5.6 V. The area of the PV array, 2 cm  2.5 cm, is small enough to be attached to home appliances. The diffusion current of the PV cell id is given by:

id  I 0 (e

eVPV 2 kT

 1)

(5)

where VPV is the output voltage of the PV cell, k is the Boltzmann constant, T is temperature in Kelvin and I0 is the reverse saturation current. I0 is measured to be 8.8 pA. It can be seen that id is zero at 0 V of VPV and that is exponentially increases as VPV increases until it is equal to iph. Using the parameters obtained as above, it was possible to obtain the T of the designed optical system. In Figure 6, the designed T and measured T at the various distances are shown. Despite the rough approximation, the measured values fit well with the designed values.

(4)

  d 2  4.5 mrad  7.5 mrad

where the denominator is the area of the truncated elliptical beam.

Fig.6. Designed and measured T with respect to the distance between the LD and the PV array.

(a)

(b)

Fig. 5. Photographs of the GaAs PV devices: (a) PV cell with and without a concentrator and (b) a PV array.

A GaAs-based PV cell was used for the laser power receiver since it has higher EQE at 830 nm than a siliconbased PV cell [13]-[14]. The GaAs PV cell generally has an open circuit voltage of 0.9-1.0 V at AM 1.5 (= 0.1 W/cm2); however, since the light intensity in our application is much lower than this value, the open circuit voltage is very low. To achieve the ACC threshold operation voltage, VACC, the number of cells in the series should be increased and the light intensity impinging on the cells should be increased. Furthermore, the size of the optical power receiver should be minimized and have a wide acceptance angle. Considering these requirements, the optical power receiver is composed of the GaAs PV cells with a plastic concentrator lens as shown in

The ACC does not work when the distance is longer than 3 m since the beam size is much larger than that of PV array area and, therefore, the effective light energy decreases. There are several ways to increase the working distance, e.g., increasing the light source’s optical power, using a higher EQE PV cell, or using more PV cells in the series. IV. EXPERIMENT RESULTS The proposed system was constructed and implemented on a 190 W commercial LCD TV that has standby power of 9.7 W. The receiver unit including the PV array was attached to the front side of the TV, which is 3 m away from remote controller. AC power consumption was measured using a digital power meter with 1 mW resolution. Figure 7 shows the PCB (9 cm  9.5 cm) of the constructed receiver unit, which includes a PV array, an IR detector, a MCU, an auxiliary AC/DC converter, an ACC and two relays.

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turned off by the LED signal of the commercial remote controller. Therefore, there is no change in the storage capacitor voltage, which is not shown here.

Fig. 7. Constructed receiver unit.

Figure 8 shows, from top to bottom, the waveforms of the storage capacitor voltage, the IR detector output, the MCU output pulse for the relay control, and AC input voltage of the appliance. The standby power consumption is initially absolute zero since the appliance and the receiver unit are physically disconnected from the AC power line by the two latch relays.

Fig. 9. The voltage waveforms when the appliance is performing the turnoff process.

When a turn-off signal is received (top trace), the MCU generates a 30 ms pulse (second trace) to reset the main relay and a 5 ms pulse (third trace) to reset the auxiliary relay. In this manner, both the appliance and the receiver unit are disconnected from the AC power line (bottom trace). The bottom trace shows that AC voltage applied to the appliance becomes zero. The top trace shows a typical voltage decay of RC circuit when the circuit is switched off. Finally, the whole system goes back into the initial standby mode, consuming absolute zero power. Without the proposed system, the TV consumes 9.7 W in standby mode, most of which is conversion loss of the main AC/DC converter at a very low load. Figure 10 shows power consumption measurement results in the time domain using our system in a dark room.

Fig. 8. The voltage waveforms observed when the appliance performs the turn-on process.

When the LD is turned on, as described in section III, the storage capacitor voltage starts to increase (top trace). The ACC then operates and the ID check unit is activated in sequence. Since the IR coded ID and command were designed to follow the laser light, the incoming coded IR signal was identified. When a valid appliance ID with a correct on signal is received (second trace), the MCU generates a 30 ms pulse (third trace) to set the main relay and the AC power line is then connected to supply AC voltage (bottom trace) to the appliance. If the ID is not correct or is not entered within 3 s, the MCU will reset the auxiliary relay to return to the initial standby mode as programmed, which makes the system insensitive to the surrounding light noise or other IR signals for adjacent appliances. Figure 9 shows the waveforms while the TV is performing the turn-off process. Contrary to the turn-on process, the TV is

Fig. 10. Power consumption of the TV with the zero standby power remote control system.

When the TV is in the off state, the power consumption is 0 W. ID check unit is activated 620 ms after the LD is turned on. For next 680 ms, the ID check unit waits for signals and operates to confirm that the ID and command are correct, consuming 220 mW. When they are correct, the TV turns on and it consumes normal operation power, 190 W.


V. CONCLUSION The home appliances have become more efficient, causing a gradual decrease in standby power consumption in recent years. However, total standby power is probably growing in the future as the number of home appliances increases. In this work, we proposed, implemented, and tested a new remote control system that decreases the standby power to absolute zero. One idea is to mount an LD on a remote controller to transmit the light energy to the remote receiver unit, while another involves using an elaborate ACC. Using incoming light power alone, the ACC can accumulate the energy, monitor the energy level, and autonomously connect the load once the accumulated energy level is sufficient to drive the load. Implementing these two ideas in a commercial appliance, a zero standby power system was constructed. It was found that, using a 15 mW laser diode, 620 ms laser illumination is enough to turn on the appliance at a 2 m distance in a completely dark room. As PV cell efficiency is improving these days, the laser aiming time and operation distance will be further improved. It is expected that this proposed system will be applied to all remotely controllable appliances in the future to conserve energy and save the environment. REFERENCES IEA, “Fact Sheet: Standby Power Use and the IEA “1 Watt Plan”,” Apr. 2007. [2] A. Meier, “A worldwide review of standby power use in homes,” Proceedings of the International Symposium on Highly Efficient Use of Energy and Reduction of its Environmental Impact, pp. 123-126, Dec. 2001. [3] H. P. Siderius, B. Harrison, M. Jakel and J. Viegand, “Standby: The Next Generation,” Proc. EEDAL, London, Jun. 2006. [4] S. Zhou and B. Liu, “Design of 80 W two-stage adapter with high efficiency and low no load input power,” Proc. APEC, pp. 728-732, Mar. 2002. [5] B. T. Huang, K. Y. Lee, and Y. S. Lai, “Design of a Two-Stage AC/DC Converter with Standby Power Losses Less than 1 W,” Proc. PCC, pp. 1630-1635, Apr. 2007. [6] J. H. Jung, J. M. Choi, and J. G. Kwon, “Novel techniques of the reduction of standby power consumption for multiple output converters,” Proc. APEC, pp. 1575-1581, Feb. 2008. [7] Y. K. Lo, S. C. Yen, and C. Y. Lin, “A High-Efficiency AC-to-DC Adaptor With a Low Standby Power Consumption,” IEEE Trans. on Industrial Electronics, vol. 55, no. 2, pp. 963-965, Feb. 2008. [8] K. Y. Lee and Y. S. Lai, “Novel circuit design for two-stage AC/DC converter to meet standby power regulations,” IET Power Electron., vol. 2, no. 6, pp. 625-634, Nov. 2009. [9] L. Chen, Z. Wang, C. Jia, F. Li, W. Hao, B. Xiao, C. Zhang and Z. Wang, “A RF remote-control transceiver with zero-standby power based on RFID technology,” Proc. PrimeAsia, pp. 243-246, Sept. 2010. [10] C. H. Tsai, Y. W. Bai, C. A. Chu, C. Y. Chung and M. B. Lin, “Design and Implementation of a Socket with Zero Standby Power using a Photovoltaic Array,” IEEE Trans. Consumer Electron., vol. 56, no. 4, pp. 2686-2693, Nov. 2010. [11] J. Kymissis, C. Kendall, J. Paradiso and N. Gershenfeld, “Parasitic Power Harvesting in Shoes,” Proc. ISWC, Los Alamitos, Calif., 1998, pp. 132-139. [12] H. S. Kim, S. M. Kang, K. J. Park, C. W. Baek and J. S. Park, “Power management circuit for wireless ubiquitous sensor nodes powered by scavenged energy,” Electron. Lett., vol. 45, no. 7, pp. 373-374, 2009.

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[13] N. Merabtinea, S. Amourachec, M. Bouaouinac, M. Zaabatb, Y. Saidic and C. Kenzaic, “An improved contribution to optimize Si and GaAs solar cell performances.” Semiconductor Physics, Quantum Electronics and Optoelectronics, vol. 7, no. 1, pp. 108-111, 2004. [14] J. Schubert, E. Oliva, F. Dimroth, W. Guter, R. Loeckenhoff and A. W. Bett, “High-Voltage GaAs Photovoltaic Laser Power Converters,” IEEE Trans. Electron Devices, vol. 56, no. 2, pp.170-175, 2009.

BIOGRAPHIES Sungmuk Kang was born in Pohang, Korea, in 1984. He received B.S. and M.S. degrees in electronic and electrical engineering from Chung-Ang University, Korea, in 2007 and 2009, respectively. Currently, he is pursuing a Ph.D. degree in electronic and electrical engineering at Chung-Ang University. His research interests include energy-harvesting circuit design, wireless sensor networks, and power management systems.

Kyungjin Park was born in Busan, Korea, in 1981. He received B.S. and M.S. degree in electronic and electrical engineering from Chung-Ang University, Korea, in 2008 and 2010, respectively. Currently, he is pursuing a Ph.D. degree in electronic and electrical engineering at Chung-Ang University. His research interests include MEMS, energy harvesting, wireless sensor networks, and power management systems.

[1]

Seunghwan Shin was born in Busan, Korea in 1983. He received a B.S. degree in electronic and electrical engineering from Chung-Ang University, Korea, in 2010. Currently, he is pursuing an M.S. degree in electronic and electrical engineering at Chung-Ang University. His research interests include energy harvesting, wireless sensor networks, and power management systems.

Keunsu Chang was born in Seocheon, Korea in 1983. He received a B.S. degree in electronic and electrical engineering from Chung-Ang University, Korea, in 2010. Currently, he is pursuing an M.S. degree in electronic and electrical engineering at Chung-Ang University. His research interests include energy harvesting, wireless sensor networks, and power management systems.

Hoseong Kim was born in Seoul, Korea, in 1957. He received a B.S. degree in electrical engineering from Seoul National University in 1980. He received M.S. and Ph.D. degrees in electrical and computer engineering from State University of New York at Buffalo in 1988 and 1992, respectively. He joined Chung-Ang University in 1993 and is currently a professor in the School of Electrical and Electronics Engineering. He is currently the head of the Circuit Design and Light Applications Laboratory. His current research interests include energy harvesting, wireless sensor networks, optical sensors and metrology, and circuit design.