Fully Integrated Direct Regulating Rectifier with Resonance Frequency Shift for Wireless Power Receivers

Transcription

1 JOURNAL OF SEMICONDUCTOR TECHNOLOGY AND SCIENCE, VOL.17, NO.5, OCTOBER, 2017 ISSN(Print) ISSN(Online) Fully Integrated Direct Regulating Rectifier with Resonance Frequency Shift for Wireless Power Receivers Chang-Jong Yim and Shi-Hong Park * Abstract Conventional methods for controlling the load-dependent output voltage require the use of an additional voltage converter. However, these methods have issues such as increase in voltage or current at the receiver side during a low load state, use of external components, increase in chip area, and reduced efficiency. This paper proposes a receiver IC that can control the load-dependent output voltage without using any additional voltage converter. The proposed IC uses a method that shifts the resonance frequency at the receiver side in the magnetic resonance wireless power transfer system, thus solving the above mentioned issues often observed in conventional methods. The proposed IC is fabricated using a 0.13-µm 90 V BCD process, and the system transfer efficiency was 54.11% at 2.5 W. Index Terms Wireless power transfer, wireless power receiver, direct regulating rectifiers, magnetic resonance, resonance frequency shift I. INTRODUCTION In recent years, research on wireless power transfer technology has gained considerable research interest owing to the popularity of smart mobile devices and wearable devices, along with new paradigms such as the Internet of Things. Further, wireless power transfer is also expected to be utilized in electric vehicles in the future. Wireless power transfer can be achieved in two Manuscript received Aug. 12, 2016; accepted Sep. 18, 2017 Dept. of Electronics and Electrical Engineering, Dankook University, Yongin-si, Gyounggi-do, , Korea icjdream@gmail.com ways: by using the magnetic induction of coils, or by using magnetic resonance. Compared to the former, the magnetic resonance method enables long-distance power transfer and simultaneous charging of multiple devices. Further, wireless power transfer using the magnetic resonance of two coils used in an antenna allows selective transmission of power according to specific resonance frequencies. Therefore, research this method has been very active in recent years [1-3]. The wireless power receiver IC that uses existing magnetic resonance methods employs a rectifier circuit to convert the received AC power into DC power and an additional voltage regulator to control the load-dependent output voltage. Fig. 1 shows the configuration of the IC for existing wireless power receivers. In general, the output voltage is regulated using additional switching regulators [4-7]. This configuration has an advantage of reliable output voltage control under load fluctuation, as shown in Fig. 1. However, a switching regulator with complex configuration can cause problems such as the inevitable increase in internal chip area and reduced efficiency. Further, EMI noise, which occurs because of the characteristics of switching regulators, and the use of external passive components, incur limitations on various application configurations. Plus, an additional circuit is required to protect against the transient state of rectifier output voltage under no-load conditions. This paper proposes a new type of circuit to control load-dependent output voltage. In addition, a circuit that can achieve high efficiency, which is one of the most important factors in wireless power receiver ICs, high cost effectiveness, and small chip size, is proposed. Section II shows the principle of wireless power transfer using magnetic resonance. Section III shows the

2 598 CHANG-JONG YIM et al : FULLY INTEGRATED DIRECT REGULATING RECTIFIER WITH RESONANCE FREQUENCY SHIFT FOR (a) (b) Fig. 1. Configuration of existing wireless power receiver IC and output voltage, and coil current waveform. circuit description. Section IV and V show the measurement results and conclusion. II. RESONANCE FREQUENCY SHIFTING Fig. 2 shows the principle of wireless power transfer using magnetic resonance. The transmitter receiver pair has a specific resonance frequency based on the characteristics of each antenna circuit. When the resonance frequencies of the transmitter and receiver match, current is induced in the coil of the power receiver device due to magnetic resonance, as shown in Fig. 2(a) [8, 9]. On the contrary, when the resonance frequencies do not match, current is not easily induced, as shown in Fig. 2(b). Thus, a wireless power transfer device using magnetic resonance can produce selective characteristics with regard to specific resonance frequency. The received power can be regulated by shifting the resonance frequency at the receiver side using the above characteristics. For example, a wireless power transfer device that has an antenna structure of series resonance type has band-pass characteristics, as Fig. 2. Wireless power transfer using magnetic resonance. (c) shown in Fig. 2(c). If a resonance frequency (f r0 ) at the receiver side matches the transmission carrier frequency (f c ) at the transmitter side, the receiver side can induce a current. However, it does not induce a current properly if the resonance frequency at the receiver side is shifted to resonance frequency (f r1 ). In the proposed IC, the received power can be selectively controlled by shifting the resonance frequency by changing the capacitor value, which forms the coil used as an antenna in the receiver and the resonance frequency [7, 8]. III. CIRCUIT DESCRIPTION Fig. 3 shows the configuration of the wireless power receiver that uses the proposed resonance frequency shift

3 JOURNAL OF SEMICONDUCTOR TECHNOLOGY AND SCIENCE, VOL.17, NO.5, OCTOBER, (a) Continuous conduction Mode (CCM) Resonant Antenna < Receiver IC > Proposed IC Direct Regulating Rectifier Vout IR IRT CR Fig. 4. Wireless power transfer using magnetic resonance. CRS S1 IRS S2 CR CRS Control Signal Control Block Voltage Sensing (b) Discontinuous Conduction Mode(DCM) Fig. 3. IC configuration of the proposed magnetic resonance wireless power receiver (a) CCM, (b) DCM. method. The proposed IC consists of a resonant antenna including a matching capacitor C R that generates the resonance frequency in the wireless power receiver; output voltage sensing and control circuit to regulate the output voltage; a direct regulating rectifier containing switches 1 and 2; and a capacitor C RS for resonance frequency shift. A simple hysteresis control method was used to regulate the output voltage, and a control circuit was configured using a comparator that has internal hysteresis. The big difference between existing IC and proposed IC is the location of added capacitors C RS. If the added capacitors C RS are connected after resonance capacitor C R as shown in Reference [6], the resonance frequency cannot be changed due to presence of rectifier capacitor C R. This configuration only changes the current path LOAD without changing the resonant frequency. However, if the added capacitors C RS are connected before resonance capacitors C R as shown in Fig. 3, the resonance frequency is changed because the added capacitor C RS is connected in parallel with resonance capacitors C R. Therefore the added capacitor C RS can change the resonance frequency. When the S1 and S2 turn on, the equivalent capacitance is changed and the resonance frequency is shifted. Therefore the power regulation in Vout is possible by controlling S1 and S2 without power loss or heating power devices. In this paper, the maximum power is limited by the breakdown voltage of the integrated switches 1 and 2. When the output load increases, the current flowing to the receiving antenna and the drain voltage of S1 and S2 also increase. This is why the voltage rating of the MOSFET used as the switch has to exceed the maximum voltage. Fig. 4 show the operation of the wireless power receiver that uses the proposed resonance frequency shift method. When operating under full load, switches 1 and 2 are OFF. The rectifier is operated in the continuous conduction mode (CCM) and power is supplied to the loads in the normal resonance frequency band. Once the full load changes to light load due to load fluctuations, the output voltage rises. Once the output voltage reaches the threshold set to V th,upper, switches 1 and 2 are turned ON by the control circuit. Thus, the received current

4 600 CHANG-JONG YIM et al : FULLY INTEGRATED DIRECT REGULATING RECTIFIER WITH RESONANCE FREQUENCY SHIFT FOR Fig. 5. IC demonstration board for the fabricated magnetic resonance wireless power receiver. (a) flows through switches 1 and 2, and the received power is reduced by the shift of the resonance frequency. A rectifier is operated in the discontinuous conduction mode (DCM) to regulate the increased output voltage. Once the load changes to full load, the output voltage drops; if it reaches the threshold set to V th,lower, switches 1 and 2 are turned OFF by the control circuit. A rectifier is operated in the CCM and it supplies power to the load, returning to the resonance frequency band to regulate the dropped output voltage. The proposed wireless power receiver IC performs the above operations iteratively, thereby regulating the output voltage without additional regulator circuits. IV. MEASUREMENT RESULTS Vout Load current Vout Coil current 5.2V 560mA (b) 40mA to 400mA 5.3V 4.9V Fig. 5 shows a demonstration board used for testing the fabricated wireless power receiver IC. Antennas for wireless power reception comply with the antenna specifications for reception mentioned in the Rezence standard developed by the Alliance for Wireless Power (A4WP) [9]. A class-e amplifier was used as a transmitter for wireless power transmission [10]. It has a transmission frequency of 6.78 MHz. The proposed wireless power receiver IC is fabricated using a 0.13-µm 90 V BCD process, and the area of the fabricated IC was 2.5 mm 2 and it is packaged with a 4 4 quad flat nonleaded package (QFN). Fig. 6 shows the output voltage of the wireless power receiver IC and coil current used as the antenna in the experiment. Agilent DSO7104B was used as the measurement device. The data were measured using 1147A-Current Probe and N2873A-Voltage Probe. The value of the output capacitor in the experiment was 4.7 µf. Fig. 6(a) and (b) show the output voltage and coil (c) (d) Fig. 6. Wireless power receiver test results (a) Waveforms at 2 W full load condition, (b) Waveforms at 0.1 W light load condition, (c) Waveforms at mA load transient condition, (d) Waveforms at ma load transient condition.

5 JOURNAL OF SEMICONDUCTOR TECHNOLOGY AND SCIENCE, VOL.17, NO.5, OCTOBER, limited to 2.5 W due to the voltage limit of internal MOSFET. Table 1 lists the data for the proposed IC and existing wireless power transfer ICs [4-6]. The proposed IC was fabricated as a fully integrated IC, which shows smaller area and better efficiency characteristics than the existing ICs. V. CONCLUSIONS Fig. 7. Efficiency characteristic graph of the fabricated IC. Table 1. Performance comparison Proposed IC ISSCC 2015[6] ISSCC 2013[4-5] Receiver structure Direct Regulating Rectifier + Buck Direct Regulating Fully integrated Yes Yes No Carrier 6.78 MHz 6.78 MHz 6.78 MHz Area 2.5 mm mm 2 N/A Receiver Efficiency System Efficiency 87.38% 84.6% 86% 54.11% N/A 55% Max W 2.5 W 6 W 6 W Operation Frequency Shift Yes No No This paper proposes a new type of fully integrated magnetic resonance wireless power receiver IC that reduced received power and regulated output voltage by shifting the resonance frequency. The system transfer efficiency was 54.11% at 2.5 W. Compared to methods that regulated output voltage using additional regulators, the proposed receiver IC has several advantages such as reduction in internal chip area due to simple configuration, and low cost due to minimal external components. In particular, the proposed receiver IC can achieve high efficiency, which is one of the most important factors in wireless power receiver ICs. Therefore, this proposed IC is expected to provide many advantages in the implementation of various applications, such as smart devices or wearable devices. current under the (a) full load with a 2 W output requirement and (b) light load conditions with a 0.1 W output requirement. The figure indicates that the output voltage is regulated to the required voltage of 5 V under full and light load conditions. In particular, it was verified that the received power is reduced under the light load condition. The maximum drive power was 2.5 W. Fig. 6(c) and (d) show the transient characteristics of the output voltage under load changing conditions. The transient characteristics of the output voltage were within 10 µs and the maximum peak-to-peak voltage was V. This follows the voltage fluctuation caused by the use of the hysteresis control mode. Fig. 7 shows the system transfer efficiency characteristic of the fabricated IC. The blue line represents the system transfer efficiency of the transmission and receiver system under the full load condition, where 54.11% system efficiency was achieved at 2.5 W. The efficiency will increase if the output power becomes higher. However, the measure of efficiency is ACKNOWLEDGMENTS The present research was conducted by the research fund of Dankook University in REFERENCES [1] R. Tseng, et al.: Introduction to the Alliance for Wireless Power Loosely-Coupled Wireless Power Transfer System Specification Version 1.0, Wireless Power Transfer, WPT 2013, IEEE International, pp.79-83, [2] X. Lu, et al.: Wireless Charger networking for mobile devices: Fundamentals, Standards, and Applications, Wireless Communications, MWC 2015, IEEE International, Vol.22, No.2, pp , [3] P. Dubal: Rezence-Wireless Charging Standard based on Magnetic Resonance, International Journal of Advanced Research in Computer and

6 602 CHANG-JONG YIM et al : FULLY INTEGRATED DIRECT REGULATING RECTIFIER WITH RESONANCE FREQUENCY SHIFT FOR Communication Engineering, IJARCCE 2015, Vol.4, No. 12, [4] J.-H. Choi, et al.: Resonant regulating Rectifiers (3R) Operating for 6.78MHz Resonant Wireless Power Transfer (RWPT), Solid-State Circuits, IEEE Journal of, Vol.48, No.12 pp , [5] J.-H. Choi, et al.: A Resonant Regulating Rectifier (3R) operating at 6.78MHz for a 6W wireless charge with 86% efficiency, Solid-State Circuits conference, ISSCC Digest od Technical Papers. IEEE International, pp.64-65, [6] K.-G. Moh, et al.: A fully integrated 6W wireless power receiver operating at 6.78MHz with magnetic resonance coupling, Solid-State Circuits conference, ISSCC Digest of Technical Papers. IEEE International, pp.1-3, [7] K. A. Grajski, et al.: Loosely-coupled wireless power transfer: Physics, circuits, standars, Microwave Workshop Series on Innovative Wireless Power Transmission: Technologies, Systems, and Applications, IMWS-IWPT 2012, IEEE International, pp.9-14, [8] B. L. Cannon, et al.: Magnetic Resonant Coupling As a Potential Means for Wireless Power Transfer to Multiple Small Receivers, Power Electronics, IEEE Transactions on, Vol.2, No.7, pp , [9] Telecommunications Technology Association, TTAE.OT (2015), [online] tta.or.kr/. [10] M. Rooij: Performance Comparison for A4WP Class-3 Wireless Power Compliance between egan FET and MOSFET in a Class E Amplifier, international Exhibition and Conference for Power Electronics, Intelligent Motion, Renewable Energy and Energy Management, PCIM Asia 2015, pp.1-8, ChangJong Yim received the B.S., M.S., degrees in the Department of Electronics & Electrical Engineering from Dankook University, Yongin-si, Korea, in 2010, 2012 respectively. From 2012, he is working toward to obtain Ph.D. degree at Dankook University. His main research interest are power ICs, automotive power ICs, wireless power transfer system, power converter circuits, gate drive IC, and integrated power electronics modules(ipems). Shihong Park received the B.S. degree in electrical engineering from Yonsei University, Seoul, Korea, in 1988, and the M.S. and Ph.D. degrees from the University of Wisconsin, Madison, in 2003 and 2004, respectively. From 1988 to 1998, he was with Samsung Electronics, Buchen, Korea, as a Senior Power IC Design Engineer. In 2004, he was a Principal Research Engineer with Fairchild Semiconductor Korea, Buchen, Korea. In March 2005, he joined the School of Electronics and Electrical Engineering, Dankook University, Seoul. His main research interests are power ICs and devices for automotive applications, LED driver circuits, power converter circuits, active gate drive topology, and integrated power electronics modules (IPEMs).