Energy transmission transformer for a wireless capsule endoscope: analysis of specific absorption rate and current density in biological tissue

This paper reports on the electromagnetic influences on the analysis of biological tissue surrounding a prototype energy transmission system for a wireless capsule endoscope. Specific absorption rate (SAR) and current density were analyzed by electromagnetic simulator in a model consisting of primary coil and a human trunk including the skin, fat, muscle, small intestine, backbone, and blood. First, electric and magnetic strength in the same conditions as the analytical model were measured and compared to the analytical values to confirm the validity of the analysis. Then, SAR and current density as a function of frequency and output power were analyzed. The validity of the analysis was confirmed by comparing the analytical values with the measured ones. The SAR was below the basic restrictions of the International Commission on Nonionizing Radiation Protection (ICNIRP). At the same time, the results for current density show that the influence on biological tissue was lowest in the 300-400 kHz range, indicating that it was possible to transmit energy safely up to 160 mW. In addition, we confirmed that the current density has decreased by reducing the primary coil's current.     

W-band investigation of material parameters, SAR distribution, and thermal response in human tissue

This investigation is divided into three parts. First, the W-band dielectric properties of different biological tissues are determined. Then, the electromagnetic field in the human eye and skin is simulated for plane-wave exposure. An analytical method is used to investigate the specific absorption rate (SAR) inside a layered model of the human skin between 3-100 GHz. Furthermore, the SAR inside a detailed model of the human eye is investigated numerically by the finite-difference time-domain method for a frequency of 77 GHz. Maximum local SAR values of 27.2 W/kg in skin tissue and 45.1 W/kg in eye tissue are found for 77 GHz and an incident power density of 1 mW/cm/sup 2/. In the third part of the investigation, the temperature changes of superficial tissue caused by millimeter-wave irradiation are measured by a thermal infrared imaging system. The exposure setup is based on a horn antenna with a Gunn oscillator operating at 15.8-dBm output power. The measurements showed a maximum temperature increase of 0.7/spl deg/C for a power density of 10 mW/cm/sup 2/ and less than 0.1/spl deg/C for 1 mW/cm/sup 2/, both in human skin (in vivo), as well as in porcine eye (in vitro). The comparison of the temperature measurements with a thermal bio-heat-transfer simulation of a layered skin model showed a good agreement.     

A regulated charge pump with small ripple voltage and fast start-up

A regulated charge pump circuit is realized in a 3.3-V 0.13-/spl mu/m CMOS technology. The charge pump exploits an automatic pumping control scheme to provide small ripple output voltage and fast start-up by decoupling output ripple and start-up time. The automatic pumping control scheme is composed of two schemes, an automatic pumping current control scheme and an automatic pumping frequency control scheme. The former automatically adjusts the size of pumping driver to reduce ripple voltage according to output voltage. The latter changes the pumping period by controlling a voltage-controlled oscillator (VCO). The output frequency of the VCO varies from 400 kHz to 600 kHz by controlling the input bias voltage of the VCO. The prototype chip delivers regulated 4.5-V output voltage from a supply voltage of 3.3 V with a flying capacitor of 330 nF, while providing 30 mA of load current. The area is 0.25 mm/sup 2/ and the measured output ripple voltage is less than 33.8 mV with a 2-/spl mu/F load capacitor. The power efficiency is greater than 70% at the range of load current from 1 to 30 mA. An analytical model for ripple voltage and recovery time is proposed demonstrating a reasonable agreement with SPICE simulation results.     

Low-power current-mode 0.9-V voltage regulator

A design for a low-power integrated 0.9-V voltage regulator for load currents up to 140 μA is presented. The circuit contains no external components and it stabilizes the voltage of a single battery cell of 1.1-1.6 V with a PSRR >40 dB over a frequency range of up to 30 kHz. The regulating circuit operates a current level and accomplishes automatic load-current limiting. Its r.m.s output noise is <4 μV over a frequency range of 10 Hz-8 kHz. The quiescent supply current is ≈40 μA     

宽带变压器在压电陶瓷驱动电源中的应用

受高压功率器件的限制,目前市场上压电陶瓷高压驱动电源较少且价格贵。变压器能够实现电压和电流的变换,合理的设计可使其在较宽的频率范围内保持良好的频率响应特性。该文研究了一种基于音频变压器的压电陶瓷高压驱动电源的实现方式,并进行了相关实验,实现了一种空载时-3 dB带宽达4 Hz~380 kHz、输出电压峰 峰值达600 V的驱动电源,可在20 kHz的频率下满负荷驱动2.5 nF的容性负载。     

Low-voltage temperature sensor for micro-power harvesters in silicon-on-sapphire CMOS

A low-voltage temperature sensor designed for MEMS power harvesting systems is fabricated. The core of the sensor is a bandgap voltage reference circuit operating with a supply voltage in the range 1-1.5 V. The prototype was fabricated on a conventional 0.5 /spl mu/m silicon-on-sapphire (SOS) process. The sensor design consumes 15 /spl mu/A of current at 1 V. The internal reference voltage is 550 mV. The temperature sensor has a digital square wave output the frequency of which is proportional to temperature. A linear model of the dependency of output frequency with temperature has a conversion factor of 1.6 kHz//spl deg/C. The output is also independent of supply voltage in the range 1-1.5 V. Measured results and targeted applications for the proposed circuit are reported.     

Design and noise analysis of a fully-differential charge pump for phase-locked loops

A fully-differential charge pump (FDCP) with perfect current matching and low output current noise is realized for phase-locked loops (PLLs). An easily stable common-mode feedback (CMFB) circuit which can handle high input voltage swing is proposed. Current mismatch and current noise contribution from the CMFB circuit is minimized. In order to optimize PLL phase noise, the output current noise of the FDCP is analyzed in detail and calculated with the sampling principle. The calculation result agrees well with the simulation. Based on the noise analysis, many methods to lower output current noise of the FDCP are discussed. The fully-differential charge pump is integrated into a 1-2 GHz frequency synthesizer and fabricated in an SMIC CMOS 0.18 μm process. The measured output reference spur is -64 dBc to -69 dBc. The in-band and out-band phase noise is -95 dBc/Hz at 3 kHz frequency offset and -123 dBc/Hz at 1 MHz frequency offset respectively.     

激光传能协同信号传输下的太阳能电池性能测试

激光无线能量传输在为远距离设备供能方面有着潜在的应用前景,在激光无线传能的同时进行激光无线通讯,具有重要的应用价值。针对砷化镓太阳能电池,对激光传能系统在无线能量传输时激光无线通讯性能进行了测试。实验采用波长808 nm激光实现砷化镓太阳能电池的能量传输,采用波长650 nm激光作为信号的传输,分别对单能量传输、单信号传输以及能量和信号同步传输三种情况下的砷化镓太阳能电池的输出特性进行了测试。结果表明:当单能量传输时,太阳能电池的性能与激光功率密度的大小密切相关,激光功率密度在54.9~90 mW/cm2范围内光电转换效率最大值为46.6%;当单信号传输时,通过测量系统的频率响应得到砷化镓太阳能电池的3 dB带宽约为3.7 kHz,并通过设计放大电路提高系统的通信性能,优化输出波形,使得系统的通信速率从10 kbps提升至240 kbps,输出电压峰峰值达到7.2 V。最后实验测量了不同激光强度下可实现的通信速率,当激光功率密度为59.5 mW/cm2时可实现140 kbps的通信速率,使得激光充电系统在无线能量传输下可以进行信号的传输。     

A low-cost fiber-optic strain gage system for biologicalapplications

A new low-cost strain measurement system has been developed for the mechanical testing of biological soft tissues. The technique creates four spots of light on a tissue sample surface by piercing the tissue sample with two pairs of small light-conducting optical fibers (one pair for each axis of a biaxial stretch), terminated by high intensity infrared emitters. A large-area photodiode, located below the tissue sample, detects the light emitted from the two pairs of light-spots. Analog and digital circuitry analyze the current signal from the photodiode to determine the position of a light-spot in real time. Each infrared emitter is sequentially cycled "on" at a rate of 3 kHz and the resulting photodiode current signal, after being converted to a voltage signal, is held by an integrated circuit sample and hold amplifier. Analog differencing of pairs of light-spot voltage signals provides a final output proportional to the separation between coaxial light-spots.     

一款用于DCDC芯片的多模式、高精度振荡器设计

设计了一款多模式的高精度振荡器,应用于开关电源芯片中,为芯片内部逻辑提供稳定的时钟源,并且具有3种工作模式,提高了整体电路的灵活性。电路中设计了低压差线性稳压器(LDO)和零温漂的电流源,使振荡器的输出频率不易受电压和温度变化的影响。同时采用可修调的技术,对电容的充电电流进行双向调整,消除了工艺带来的误差。该电路基于CSMC 0.25μm 2P5M工艺进行设计,采用HSPICE进行仿真,结果表明,在3.0~6.0 V输入电压范围内,输出频率变化1.1 kHz,变化率为0.22%;在-55~125℃温度范围内,输出频率变化2.1 kHz,变化率为0.41%。     

A novel soft-switched PWM current source inverter with voltageclamped circuit

This paper develops a new series resonant (current resonant) DC link inverter with a voltage clamped circuit. The proposed circuit has a fixed pulse frequency operation. The fixed pulse frequency at 20-50 kHz enables the system to work without audible noise, and to involve the much smaller-sized DC inductance and output capacitors compared with hard-switched current source inverters. The proposed circuit has a voltage clamped circuit which could control the voltage stress of the switches. In this paper, explanations of the new circuit configuration, the simulation, design considerations, and some experimental results are included     

Single switch dual output DC-DC converter performance

The performance of the single-switch dual-output DC-DC converter is evaluated. This converter regulates two independent DC outputs supplied from a single DC voltage source using a power semiconductor switch. Two discrete proportional feedback control loops regulate the duration of on switching and off switching. The duty cycle of the switch controls one output voltage, supplied from a low-pass filter, while the switching frequency regulates the other output voltage, supplied from a higher-frequency bandpass filter. The control algorithm is implemented with an Intel 8096 microcontroller. The experimental data demonstrate the actual circuit performance and confirm the simulation results. Both experiments and simulation show that an increase in the load current on the 12 V output results in an increase in the duty cycle, whereas an increase in the load current on the 5 V output results in a change in the switching frequency. The experimental prototype demonstrates operation over a load current range from about 40% to 100% with a ±25% variation in the 24 V input. Full load currents are 12 A and 2.5 A on the 12 V and 5 V outputs, respectively. The switching frequency ranged from approximately 29 kHz to 264 kHz, and the duty cycle ranged from 0.35 to 0.72     

Localized electrical nerve blocking

Localized electrical nerve blocking was investigated in computer simulation and in vivo trials for sinusoidal frequencies between 5 and 20 kHz. Computer simulations indicated that a localized transmission block of the axons could occur in each of the axon models. An approximation of nerve stimulation was derived from individual axon simulations conducted over axon diameters of 5-15 microm and electrode to axon distances of 0.25 to 2.0 mm. Examination of the membrane voltage and ionic gate potentials indicated that the block could be attributed to an elevated membrane voltage. The elevated membrane voltage could prevent conduction of action potentials through the region of the sinusoidal currents. At lower amplitudes, the sinusoidal current could stimulate the axon and generate a continuous series of action potentials. In vivo trials demonstrated that the sinusoidal frequencies of greater than 10 kHz would cause a localized block in rats. Sinusoidal frequencies below 5 kHz would lead to a reduction in muscle force that appeared to be caused by depletion of transmitter at the neuromuscular junction. As indicated by the computer models of rat nerves, the endplate depletion block occurred at a lower frequency (below 5 kHz) than the block (above 10 kHz). A partial block of the axon was demonstrated, suggesting that sinusoidal currents could be used to provide selective stimulation if they are combined with distal electrical stimulation.     

Two-wire bridge-to-frequency converter

An integrated two-wire bridge-to-frequency converter is presented for use as a remote-signal conditioner for sensor bridges such as strain-gauge bridges of platinum-wire temperature-sensing bridges. The converter has a sensitivity on the order of 1 Hz per 1-/spl mu/V/V relative bridge output. A center frequency of 10 kHz allows the application of an untrimmed bridge with an imbalance up to /spl plusmn/10000 /spl mu/V/V. The instability is less than 10/SUP -4/ per Kelvin and per 1-V supply-voltage variation. The untrimmed transfer inaccuracy is lower than 1%. The linearity error is lower than 0.01%. Different bridge readout functions can be chosen by different circuit configurations. The converter can be connected to a single supply voltage. The frequency output is modulated on the supply current. The supply voltage is 12-24 V.     

新一代GaN基DC/DC Buck电源模块测试与分析

文中对宜普电源转换公司(EPC)Buck转换器EPC9107进行参数测试与分析。测试结果表明,当EPC9107电源模块工作于开关频率1000 kHz、宽幅输入电压12~28 V时,输出电压恒定3.3 V,输出电流约为0~16 A,效率最高约为96.1%,功率密度约为14 W·cm-3,转换时间小于4 ns,具有良好的抗干扰度和瞬态响应,纹波小于20 mV。该模块的整体性能均优于当前硅基DC/DC电源模块。     

一种高精度BiCMOS电流模带隙基准源

采用Xfab0.35μmBiCMOS工艺设计了一种高电源抑制比（PSRR）、低温漂、输出0.5V的带隙基准源电路。该设计中,电路采用新型电流模带隙基准,解决了传统电流模带隙基准的第三简并态的问题,且实现了较低的基准电压;增加了修调电路,实现了基准电压的微调。利用Cadence软件对其进行仿真验证,其结果显示,当温度在-40～＋120℃范围内变化时,输出基准电压的温度系数为15ppm/℃;电源电压在2～4V范围内变化时,基准电压摆动小于0.06mV;低频下具有-102.6dB的PSRR,40kHz前电源抑制比仍小于-100dB。     

Simulation of induced current densities in the human body atindustrial induction heating frequencies

At industrial workplaces in the vicinity of induction heating and melting devices, workers are exposed to strong magnetic fields. Up until now, little knowledge about the coupling of external fields into the human body at low frequencies existed. This paper provides numerical investigations to clarify the ratio between external homogeneous magnetic fields and induced current densities inside the human body in the frequency range from 250 Hz up to 10 kHz. The finite-difference time-domain (FDTD) method is used to calculate the induced current density in a realistic inhomogeneous 1 cm resolution human body model with appropriate tissue parameters. The magnitude of the external magnetic field equals the reference value for occupational exposure in the current guideline of the International Commission on Nonionizing Radiation Protection (ICNIRP). It was found that the calculated maximum current densities inside the body may exceed the basic restrictions of the ICNIRP guideline at least up to a factor of two. Finally, the suitability of the human body model for dosimetric investigations is discussed in view of fine-resolution models presented in the literature     

An implantable wireless bidirectional communication microstimulator for neuromuscular stimulation

This paper presents the integrated circuit design for a wireless bidirectional transmission microstimulator. This implantable device is composed of an internal radio-frequency (RF) front-end circuit, a control circuit, a stimulator, and an on-chip transmitter. A 2-MHz amplitude-shift keying modulated signal, including the power and data necessary for the implantable device, is received, and a stable 3-V dc voltage and digital data will be extracted to further execute neuromuscular stimulation. The current-mode microstimulator can produce a bidirectional output current with 8-bit resolution for stimulation. The maximum stimulation current is 1 mA while the stimulation frequency is from 20 Hz to 2 kHz and the pulsewidth of stimulation current is from 150 to 500 /spl mu/s. Furthermore, the system can acquire the biological sensing signal by means of an on-chip transmitter. Most of the signal processing circuits have been designed with low-power schemes to reduce the power consumption, and the performance is also conformed to the requirements of the microstimulator. All of the circuits except for the RF link are combined in a single chip and implemented in TSMC 0.35-/spl mu/m 2P4M standard CMOS process.     

基于高频高压交流母线多组输出直流电源的研制

本电源是基于高频高压交流母线具有多组输出的直流电源，它具有高达200kHz的开关频率，后级的整流电路由于高频交流母线的存在，使得变压器和电感的设计变得简单，滤波电容的选择也更容易。本电源由PFC电路提供400V的高压直流输入，再由MOSFET组成全桥逆变电路，在固定额率的PWM发生电路和IR2110 MOSFET驱动电路作用下，只加—个谐振电感就可实现开关管的零电压开通，可在大大降低开关损耗和噪声的同时实现直流交流的变换。整流部分采用倍流整流电路以提高原边电压的利用率，可输出低压大电流。由于采用肖特基管，—方面可使得二板管的损耗可以接受，另外—方面还避免了采用同步整流电路所面临的电路结构复杂和驱动困难。     

Integrated ZVS DC–DC converter with continuous input current and high voltage gain

An integrated zero-voltage-switching (ZVS) DC–DC converter with continuous input current and high voltage gain is proposed. The proposed converter can operate with soft switching, a continuous inductor current and fixed switching frequency. The voltage stress of the power switches is relatively low compared to the output voltage. Moreover, soft-switching characteristic of the proposed converter reduces switching loss of active power switches and raise the conversion efficiency. The reverse-recovery problem of output rectifiers is also alleviated by controlling the current changing rates of diodes with the use of the leakage inductance of a coupled inductor. The operation and performance of the proposed DC–DC converter were verified on an 115?W experimental prototype operating at 100?kHz.