Recordings of Bioelectric Potentials with Glass Microelectrodes: Limitations of Unity-Gain Follower with Buffer

It is possible to design amplifiers with virtually no input capacitance. As shown in the sequel, this feature, however, is not by itself sufficient to insure faithful recording of fast transmembrane potentials with glass microelectrodes.     

超低功耗Q波段低噪声放大器芯片的设计和实现

采用GaAs赝配HEMT单片微波集成电路(MMIC)工艺和堆栈偏置技术设计实现了一款Q波段低噪声放大器(LNA)芯片.该放大器采用4级级联的堆栈偏置拓扑结构,前两级电路在确保较低输入回波损耗的同时优化了放大器的噪声系数,后两级电路则采用最大增益的匹配方式,确保放大器具有良好的增益平坦度和较小的输出回波损耗.该LNA芯片最终尺寸为3 250 μm×1 500 μm,实测结果表明在40～46 GHz工作频率内放大器工作稳定,小信号增益大于23 dB,噪声系数小于3.0 dB,在4.5V工作电压下消耗电流约6 mA.此外,在片实测结果和设计结果符合良好.     

A low-voltage micropower JFET/bipolar operational amplifier

A single cell supply (operable down to 1.2 V) micropower operational amplifier using compatible low pinchoff voltage JFET's (V/SUB p/=0.4 V) in conjunction with standard bipolar technology has been developed. The subvolt pinchoff JFET's have proved useful in the common-mode feedback-assisted biasing of a simple p-n-p input stage to permit single supply operation, the design of a low-voltage high-performance current mirror and a differential to single-ended converter. The amplifier exhibits excellent ac performance (unity gain slew rate=0.25 V//spl mu/s, unity gain bandwidth=850 kHz) with low power dissipation (245 /spl mu/W).     

2-µm Gate-length enhancement mode InGaAs/InP:Fe-JFET's with high transconductance

Investigations of enhancement mode InGaAs junction field-effect transistors (JFET's) grown on InP:Fe-substrate by liquid-phase epitaxy (LPE) are reported. The JFET's with 2-µm gate length and 190- µm gate width show a threshold voltage of 0.4 V, a low drain current of < 10 µA at 0-V gate-source voltage and a maximum transconductance of 105 mS/mm. The measured transconductances of enhancement mode InGaAs/InP:Fe JFET's with different gate lengths but with the same gate width and threshold voltage decrease proportional to the inverse gate length as expected from a constant drift mobility FET model.     

Membrane noise and intercellular communication

Voltage noise has been recorded with intracellular glass microelectrodes from spheroidal aggregates of embryonic heart cells in culture. Beating was suppressed with tetrodotoxin. Input resistance and noise decreased as external potassium increased. Cross correlation of noise from two cells in an aggregate was used to measure their electrical coupling. Current injected through a third electrode permitted an independent measure of intercellular communication. Coupling resistance was found to be less than 10 percent of the aggregate input impedance, and to be frequency-independent from dc to 160 Hz.     

High-voltage junction-gate field-effect transistor with recessed gates

A new recessed-gate structure for vertical-channel junction field-effect transistors (JFET's) is described together with a self-aligned gate-source process developed to fabricate these devices. Using this technology, devices with groove depths ranging from 8 to 18 µm have been fabricated. The characteristics of these devices is described as a function of the groove depth. It has been found that the devices display pentode-like characteristics at low gate voltages and triode-like characteristics at high gate voltages. The blocking gain has been found to increase with groove depth. However, this is accompanied by an increase in the on-resistance and a decrease in the saturated drain current. Devices with gate breakdown voltages of up to 600 V have been fabricated with the recessed-gate structure. These high-voltage field-effect transistors (FET's) have a unity power gain cutoff frequency of 600 MHz and gate turn-off times of less than 25 ns.     

A new lateral field emission device using chemical-mechanicalpolishing

A polysilicon lateral field emission device using chemical-mechanical polishing (CMP) is proposed and experimental results on the first prototype are reported. In this method, dry oxidation process determines the interelectrode gap. Thus, it is relatively easy to form electrode gaps with dimensions less than 1 μm. Also, the process allows for good uniformity and reproducibility in controlling the interelectrode gap. The turn-on voltage of the fabricated device with interelectrode gap of 3500 Å is as low as 5.4 V and the emission current is as high as 9 μA at 9.3 V. From the Fowler-Nordheim (FN) equation, field emitting area (α) and field enhancement factor (β) are estimated to explain the low turn-on voltage and the high emission current. The emission current fluctuation is about ±4% for 25 min     

Capacitive design considerations for film-type and integrated circuits

A critical survey of capacitive effects in thin-film structures was made and design parameters to assess interelectrode coupling in integrated circuits were determined. By applying judiciously conformal mapping techniques, procedures and graphs were developed which permit evaluation of interfilm capacitances for many types of plane-parallel and cylindrical geometries. Representative designs of integrated circuits were analysed to demonstrate the effectiveness of these techniques.     

Polarization independent InP WDM multiplexer/demultiplexer module

We report the design, fabrication, packaging, and characterization of a polarization independent integrated optical InP multiplexer/demultiplexer module. The device is based on a vertically etched diffractive grating and separates four channels with 4 spacing in the 1.55 μm window. An n^-/n⁺-InP layer structure with very low birefringence results in a shift of the passbands between transverse electric (TE) and transverse magnetic (TM) polarization of less than 0.1 nm. With a self-aligned flip-chip mounting technique light is optically coupled from the input and output waveguides to an array of lensed single mode fibers with a coupling efficiency of more than 80%. The packaging includes temperature control that allows fine tuning of the channel passbands over 5 nm. Optical crosstalk is always better than -17 dB and fiber to fiber losses of 15 dB are achieved. The module has been successfully implemented in a 4×2.5 Gb/s WDM transmission system     

Characterization of signals and noise rejection with bipolarlongitudinal intrafascicular electrodes

Longitudinal intrafascicular electrodes (LIFEs) are fine electrodes threaded into the extracellular space between axons in peripheral nerves or spinal roots. The authors are developing these electrodes for application in functional electrical stimulation and in basic physiology. An area of concern in chronic recording application of LIFEs is the possibility of electromyogram and other external noise sources masking the recorded neural signals. The authors characterized neural signals recorded by LIFEs and confirmed by three independent methods that increasing interelectrode spacing for bipolar LIFEs increases signal amplitude. The spectrum of neural signal from bipolar and monopolar LIFE lies between 300 Hz and 10 kHz. The amplitude of the spectrum increases with increasing interelectrode spacing, although the distribution is not affected. Single unit analysis of LIFE recordings show that they record selectively from units closest to the electrode active site. Units with conduction velocities ranging from 50-120 m/s were identified. Extraneural noise, as stimulus artifact or electromyogram, is much reduced with bipolar LIFE recording, as compared to monopolar recordings. Relative improvement in neural signal to extraneural noise increases with interelectrode spacing up to about 2 mm. Since there is no further improvement beyond 2 mm, the authors conclude that the preferred interelectrode spacing for bipolar LIFEs is 2 mm     

一种Ka波段三路波导功率分配/合成器的设计

提出了一种波导三路功分器结构,该功分器采用E面T型缝隙耦合结构来实现功分比的调节。通过调节耦合缝隙以及感性膜片,使输入阻抗匹配并且实现等功率同相位的三路功分输出。为了实现功率合成,采用对称的两个三路功分器进行背靠背级联实现功率合成网络,仿真结果显示出良好的驻波效果和极低的插损。最终对加工出的实物进行测量,在32.5~36 GHz频段内实现了输出功率幅度不平衡度小于0.5 dB的良好效果。通过背靠背连接两个功分器实现了在33.3~35.3 GHz带宽内插损小于0.3 dB的功率分配/合成网络。     

Nanostructured surface modification of ceramic-based microelectrodes to enhance biocompatibility for a direct brain-machine interface

Many different types of microelectrodes have been developed for use as a direct Brain-Machine Interface (BMI) to chronically recording single neuron action potentials from ensembles of neurons. Unfortunately, the recordings from these microelectrode devices are not consistent and often last for only a few weeks. For most microelectrode types, the loss of these recordings is not due to failure of the electrodes but most likely due to damage to surrounding tissue that results in the formation of nonconductive glial-scar. Since the extracellular matrix consists of nanostructured microtubules, we have postulated that neurons may prefer a more complex surface structure than the smooth surface typical of thin-film microelectrodes. We, therefore, investigated the suitability of a nano-porous silicon surface layer to increase the biocompatibility of our thin film ceramic-insulated multisite electrodes. In-vitro testing demonstrated, for the first time, decreased adhesion of astrocytes and increased extension of neurites from pheochromocytoma cells on porous silicon surfaces compared to smooth silicon sufaces. Moreover, nano-porous surfaces were more biocompatible than macroporous surfaces. Collectively, these results support our hypothesis that nano-porous silicon may be an ideal material to improve biocompatibility of chronically implanted microelectrodes. We next developed a method to apply nano-porous surfaces to ceramic insulated, thin-film, microelectrodes and tested them in vivo. Chronic testing demonstrated that the nano-porous surface modification did not alter the electrical properties of the recording sites and did not interfere with proper functioning of the microelectrodes in vivo.     

Integrated self-scanning light-emitting device (SLED)

The fabrication of monolithically integrated self-scanning light-emitting device (SLED) on a GaAs substrate and its performance are described. The SLED consists of integrated light-emitting thyristors whose turn-on voltages interact with each other through coupling diodes or resistors. Light-emitting states are automatically transferred by input clock pulses without using external shift registers. The resistors are made of a Cr-SiO cermet film, and the coupling diodes are made in part with p-n layers of thyristors. The integrated SLED is fabricated in eight photolithographic steps. High-speed operation, more than 10 MHz, can be achieved due to its simple structure and high-density packaging. It is expected that this SLED will be a key device in future large-scale optoelectronic integrated circuits     

一款集成驱动放大器的低变频损耗混频器设计

采用0.5μm GaAs工艺设计并制造了一款单片集成驱动放大器的低变频损耗混频器.电路主要包括混频部分、巴伦和驱动放大器3个模块.混频器的射频(RF)、本振(LO)频率为4～7 GHz,中频(IF)带宽为DC～2.5 GHz,芯片变频损耗小于7 dB,本振到射频隔离度大于35 dB,本振到中频隔离度大于27 dB.1 dB压缩点输入功率大于11 dBm,输入三阶交调点大于20 dBm.该混频器单片集成一款驱动放大器,解决了无源混频器要求大本振功率的问题,变频功能由串联二极管环实现,巴伦采用螺旋式结构,在实现超低变频损耗和良好隔离度的同时,保持了较小的芯片面积.整体芯片面积为1.1 mm×1.2 mm.     

Integrated linear giga-ohm resistance using current scaling

Integrated grounded resistors of very large value are essential circuit elements for the design of compact filters with very low cut-off frequencies. A typical application of such filters is the rejection of DC voltages in amplifier circuits especially in physiological recording systems exhibiting electrode offset and low-frequency drift. In this letter, the implementation of a giga-ohm resistance is presented using a conventional fixed-gain OTA and a cascade of weak-inversion current scalers. The circuit yields a short design time, small power and area consumption as well as high linearity. A test circuit having an area of 0.011 mm² integrated in 0.35 μm CMOS is presented which yields a 41 Hz cut-off frequency, 1 V input range and less than −52 dB THD when connected to an integrated 1 pF capacitor, making it a suitable solution for the rejection of mains interference and offset in wearable biomedical applications.     

Harmonic resonant DC-DC converter for low coupling transformers

A new harmonic resonant DC-DC converter is proposed. The harmonic resonant converter is related to the multi-resonant converter and is used for transformers with low coupling. Two harmonic frequencies are present during any resonant state and the switch voltage can be less than two times the input voltage     

采用电流复用拓扑的宽带收发一体多功能电路

基于标准的GaAs赝配高电子迁移率晶体管(PHEMT)单片微波集成电路(MMIC)工艺设计并制备了一款宽带收发一体多功能电路芯片.该多功能芯片包含了功率放大器、低噪声放大器和收发开关.放大器采用电流复用拓扑结构实现了低功耗的目标.收发开关采用浮地结构避免了使用负电源.芯片在14～ 24 GHz工作频率的实测结果显示:接收支路噪声系数小于3.0dB,增益大于18 dB,输入及输出电压驻波比(VSWR)均小于2.0,1 dB压缩点输出功率大于0 dBm,直流功耗为60 mW;发射支路增益大于21 dB,输入输出VSWR均小于1.8,1dB压缩点输出功率大于10 dBm,直流功耗为180 mW.芯片尺寸为2 600 μm×1 800 μm.该多功能收发电路的在片测试结果和仿真结果一致,性能达到了设计要求.     

Coupling of NRD-Guide Filled with Low Permittivity Dielectric Between Waveguides

A new version of NRD-guide coupling structure is proposed in which a low permittivity dielectric is filled between the coupling waveguides. It takes full advantage of the common NRD-guide with more flexibility. The choice of different dielectric materials can optimize the required performance. The corresponding coupling characteristics are analyzed. Some examples are given to show the new coupling characteristics. An important feature is the enhanced coupling between the waveguides and increased attenuation in the transverse direction, and this implies a size reduction and enhanced EMC capability. Furthermore, the filling of the low dielectric material between the coupling waveguides makes the structure an integrated unit and especially suitable for realization by micro-electromechanical system (MEMS) or by microwave integrated circuits.     

Optical frequency conversion device with asymmetric κ-DBRstructure

An optical-frequency conversion device is fabricated, using monolithically integrated distributed Bragg reflector (DBR) mirrors with different coupling coefficients at the outer sides of the active and the saturable absorber regions. The input-end DBR mirror has a higher coupling coefficient than that of the output-end DBR mirror. The converted light is reflected by the input-end DBR mirror and is emitted only from the output end of the device. This device successfully performs optical frequency conversion when the input TM-polarized light has a wavelength within the wavelength range for which the reflection of the input-end DBR mirror is fairly high for TE-polarized light. The ratio of the converted-light output power for TE-polarized light from the input end to that from the output end is less than -30 dB     

Sensitivity limits of long-wavelength monolithically integratedp-i-n JFET photoreceivers

Noise characteristics and factors which limit the sensitivity of long-wavelength monolithically integrated photoreceivers using InGaAs p-i-n photodiodes (PD) and InGaAs junction-held-effect transistors (JFET's) were analyzed with regard to the input-noise current and the open-loop gain. Effects of the JFET gate length and the parasitic capacitance on the sensitivity were also clarified. Three types of photoreceivers were fabricated by using metal organic vapor phase epitaxy (MOVPE)-grown crystals and Be-ion implantation technology. The receiver using a cascode input stage had an extremely high sensitivity (-35.4 dBm) for a 622-Mb/s NRZ, 13-μm-wavelength signal. The sensitivity of the other two receivers using an inverter input stage was moderate, -33.6 dBm for a multipower supply input stage and -31.4 dBm for a single power supply input stage