电极电位与放大器的前级设计

在生物电信号的采集放大过程中,电极电位常可引起不易察觉的干扰和信号畸变,影响正常波形的判断识别。主要影响机制为：放大器前级部分阻塞、“高频斩波”式干扰、分布电容变化干扰及电极引线漏中噪声。作者提出电极电位抵消和前级高频预滤波电路,并结合前级隔离、驱动屏蔽技术应用于放大器的的前级设计,可大大提高放大器对电极电位的耐受能力。基本消除电极电位的影响。     

低噪声、低纹波头皮脑电信号采集的前端电路

基于SMIC 0.18 μm CMOS工艺设计了一种由前置放大器、纹波抑制电路、增益可编程放大器和外置低通滤波器组成的低噪声头皮脑电信号采集前端电路。其中前置放大器采用斩波技术来降低低频噪声和失调电压,其结构为电容耦合的斩波稳定放大器,其有源放大部分由折叠式共源共栅级和共源级构成的两级全差分放大器构成,以获得较高的开环增益;同时在前置放大器后引入了阻容耦合电路来抑制在斩波频率处产生的纹波。可编程增益放大器采用可调电容阵列构成的电容负反馈放大器以实现增益逐级可调。Spectre后仿真结果表明,前置放大器的增益为40 dB,共模抑制比可达131 dB,电源抑制比90 dB,输入等效噪声772 nV/sqrt(Hz)@100 Hz;可编程增益放大器的增益分别为12、20、25 dB;低通滤波器的截止频率为1 kHz;纹波抑制电路对在斩波频率处的纹波具有400倍的抑制效果。该前端电路的总增益为40~65 dB,通频带为1 Hz~1 kHz。     

光耦功率放大技术在CT超低剂量扫描的研究

目的将全新的光电耦合高电压强电流放大处理技术用于CT机的前置放大处理中,隔离噪声和高电压大电流放大图像信号,实现超低剂量扫描,高清晰成像。方法将光电耦合放大器制作成射线剂量仪,并用CT机等超低剂量120KV、3-6mA…对其曝光,并与标准射线剂量仪校准,使其输出值不仅为射线剂量值,更能显示为高电压和大电流的优质图像信噪比。结果超小电流扫描经探测和光耦放大后最大值为87.5V和0.96A,而噪声电压为0.13μV、电流仅为0.02μA,给超低剂量扫描和传输处理时的功耗及高电压的宽动态范围显示留了很大空间。结论 CT超低剂量扫描时光耦放大器可在源头彻底隔离各种噪声并超高倍放大、高电压大电流输出图像信号,可保证高清晰高分辨率成像。     

基于相关双采样技术的CCD信号处理

目的电荷耦合器件（charge coupled device,CCD）的输出信号中含有多种噪声,其中主要是复位噪声,所以在CCD信号采集系统中,一项关键技术就是去除或削弱噪声。方法本文详细介绍了CCD复位噪声的产生机理,设计了基于相关双采样技术（correlated double sampling,CDS）的CCD信号处理电路。结果通过实验验证上述信号处理电路可以有效抑制CCD噪声。结论相关双采样技术在一定程度上抑制了CCD复位噪声,有利于后续CCD信号的采集与传输。     

集成运算放大器在检测微弱生理信号中的一种用法

本文介绍了由集成运算放大器组成的低噪声、高精度前置放大器的一种设计方法。用于检测微弱生理信号时,可获得良好的低噪声性能,其最小噪声系数F_min<2,且具有设计简单、调试方便、综合性能好等特点。文中还给出了设计实例。     

5—5 生物弱信号检测用三运放前置放大器高CMRR的设计与分析

微弱生物信号测量通常是在很大的共模干扰情况下进行的,因此如何设计高共模抑制比(CMRR)的前置放大器至关重要。随着集成电路技术的发展,生物弱信号测量中广泛采用三运放仪器放大器作前置放大。三运放输出级采用单端输出,因此系统CMRR实际取决于三运放。以住的文献在论及三运放CMRR时考虑因素较少,或者只突出了某个方面因素的影响。本文拟在对三运放进行分析的基础上,对影响其CMRR的因素进行较全面的讨论,同时结合我们研制微弱生物信号检测系统的实际对如何进行     

多功能中医针灸治疗仪的研制与应用

目的 研制一种既能进行电针和体外按摩治疗又能进行灸疗的多功能针灸治疗仪。方法　电针和体外按摩采用非对称双极性零电荷积累的输出设计，灸疗由微处理控制施灸温度，仪器工作过程由微处理器控制。结果 多功能针灸治疗仪具有多刺激模式的电针和体外按摩输出，治疗时无疼痛感，灸疗温度可定量调节，安全可靠。结论 试用结果表明，该仪器临床治疗功能齐全，疗效可靠，患易于接受，可替代传统中医针灸疗法。     

临床条件下桡动脉搏的测量

为了诊断的目的,常分析桡动脉脉搏记录。这种分析可用于诊断血管疾病。最近提出的压力的时间微商可能是心脏喷射动作和瓣膜功能的灵敏指标。Starr及其同事用电子学方法使压力波微分,但这种办法增加了噪声水平。作者运用换能器和有关电学方法,能够在相当小的噪声情况下对高频成分进行观察。仪器情况已另有报导。我们从一组伸舌样迟钝病对象取得的数据,可以作为本设计的临床评价的一部分。此数据与从同一医院的另一组病人得到的数     

脑电信号采集预处理电路设计

目的:设计一种脑电信号采集预处理电路,从大量的噪声中提取微弱的脑电信号.方法:脑电信号很微弱,一般在5μV～100μV之间,需设计放大倍数在10000～50000的可调电路.同时,脑电信号还处于极化电压、高频干扰、50Hz工频干扰等噪声干扰之下,为了消除干扰,需设计前置放大电路、高通滤波器、低通滤波器和50 Hz陷波器.出于安全考虑,还需设计隔离电路.特别是前置放大电路,是整个电路的关键.结果:经过各个模块的处理,得到了高质量的脑电信号,以便后续应用.结论:实验表明,该设计能较好的把微弱的脑电信号提取出来,有较好的适用价值.     

玻璃体液钾钠离子浓度便携式测定仪器的初步设计

目的：介绍一种玻璃体液钾钠离子浓度便携式测定仪器的设计。方法：采用离子选择电极作为信号转换元件来检测离子浓度,对电极进行温度补偿和噪声分析,设计玻璃体液钾钠离子浓度便携式检测仪器。结果：经初步测试,该检测仪器能够现场快速检测玻璃体液钾钠离子的浓度。结论：更换相应的离子电极和运放的反馈电阻,就可完成其它离子的检测,进而实现现场快速地测量人死后玻璃体液化学成分的浓度。     

Noise characteristic design of CMOS source follower and voltage amplifier for active semiconductor microelectrodes for neural signal recording

A noise performance design method for the pre-amplifiers of an active neural probe is given. The on-chip circuitry of the active neural probe consists of CMOS devices that show high-/ low-frequency noise, so that the device noise can become dominant. Analysis of the signal-to-device-noise ratio (SDNR) for the CMOS source follower buffer and two-stage differential voltage amplifier is given. Closed-form expressions for the output noise power are derived and exploited to tailor the parameters that are controllable during circuit design. The output SDNR is calculated considering the real extracellular action potentials, the electrode-electrolyte interface and the noise spectrum of CMOS devices from typical foundries. It is shown that the output device noise power can be much higher than the output signal power if the devices at the input stage of the pre-amplifier are made as small as given fabrication technology permits. Quantitative information of the circuit parameters to achieve an SDNR higher than 5 for neural spikes with 60μV amplitude are provided for both preamplifier types.     

A low noise isolated amplifier system for electrophysiological measurements: basic considerations and design

An instrumentation amplifier for medical and biological research applications is described. It consists of an isolated preamplifier with a high signal/ noise ratio and a computer or microprocessor controlled main amplifier that incorporates variable highpass and lowpass filtering. The preamplifier includes an input stage, a compensation circuit for electrode offset voltage and an isolation amplifier. Recently introduced ultra low noise operational amplifiers used in the input stage ensure good noise behaviour. Isolation is obtained with an inductive isolation amplifier, which also delivers the supply voltages for the input stage. Accordingly, battery power is not needed, in contrast with optically isolated amplifiers. The main amplifier has computer control for gain, lowpass cut-off frequency and highpass cut-off frequency settings. This features dynamic changes in signal conditioning and data acquisition by the same computer that collects the data. Data acquisition and noise behaviour are discussed. The filter configuration is designed in such a way that several user-defined options can be implemented on the same circuit board. The trade-off between the order of the lowpass filters, their roll-off, and the sampling rate which is used in the subsequent computing system, are of major importance and will be discussed. The amplifier system is at present in sue in laboratories of neurology (BEP, EEG), opthalmology (VEP, EOG, ERG) and cardiology (noninvasive His bundle recordings) from which some results will be presented. The amplifiers form a part of a microprocessor-controlled data acquisition system.     

A prototype high-purity germanium detector system with fast photon-counting circuitry for medical imaging

A data-acquisition system designed for x-ray medical imaging utilizes a segmented high-purity germanium (HPGe) detector array with 2-mm wide and 6-mm thick elements. The detectors are contained within a liquid-nitrogen cryostat designed to minimize heat losses. The 50-ns pulse-shaping time of the preamplifier electronics is selected as the shortest time constant compatible with the 50-ns charge collection time of the detector. This provides the detection system with the fastest count-rate capabilities and immunity from microphonics, with moderate energy resolution performance. A theoretical analysis of the preamplifier electronics shows that its noise performance is limited primarily by its input capacitance, and is independent of detector leakage current up to approximately 100 nA. The system experimentally demonstrates count rates exceeding 1 million counts per second per element with an energy resolution of 7 keV for the 60-keV gamma ray photon from 241Am. The results demonstrate the performance of a data acquisition system utilizing HPGe detector systems which would be suitable for dual-energy imaging as well as systems offering simultaneous x-ray transmission and radionuclide emission imaging.     

A miniature three-channel preamplifier for unit recording in freely moving animals

A miniature, three-channel high input and low output impedance preamplifier is described for extracellular unit recording in freely moving animals. A MOSFET and an integrated circuit operational amplifier provide the two stages of each of the three amplifiers. The overall gain is approximately 200, down 6db at 1.5 Hz and 5 kHz. The peak-to-peak broadband noise amplitude with a source resistance of 10 kΩ is 10μV.     

基于AVR的高精度医用激光功率密度计

目的 设计一种高精度的医用激光功率密度计,用于测量激光在临床医学上的功率密度,以便更好地将激光应用于临床.方法 采用热释电探测器将激光信号转换为可处理的电信号,设计与探测器相匹配的前级放大滤波电路及控制显示电路;采用C语言进行软件编程,软硬件相结合,研制一种基于AVR单片机控制的高精度医用激光功率密度计.结果 功率密度计可测量的最小功率密度为1 mW/cm2,误差为2％,可满足临床上医用激光功率密度测量的参数要求.结论 功率密度计精度高、误差小、稳定性好,能够精确测量激光功率密度大小.     

Pushing the limits of high‐resolution functional MRI using a simple high‐density multi‐element coil design

Recent studies have shown that functional MRI (fMRI) can be sensitive to the laminar and columnar organization of the cortex based on differences in the spatial and temporal characteristics of the blood oxygenation level‐dependent (BOLD) signal originating from the macrovasculature and the neuronal‐specific microvasculature. Human fMRI studies at this scale of the cortical architecture, however, are very rare because the high spatial/temporal resolution required to explore these properties of the BOLD signal are limited by the signal‐to‐noise ratio. Here, we show that it is possible to detect BOLD signal changes at an isotropic spatial resolution as high as 0.55 mm at 7 T using a high‐density multi‐element surface coil with minimal electronics, which allows close proximity to the head. The coil comprises of very small, 1 × 2‐cm², elements arranged in four flexible modules of four elements each (16‐channel) that can be positioned within 1 mm from the head. As a result of this proximity, tissue losses were five‐fold greater than coil losses and sufficient to exclude preamplifier decoupling. When compared with a standard 16‐channel head coil, the BOLD sensitivity was approximately 2.2‐fold higher for a high spatial/temporal resolution (1 mm isotropic/0.4 s), multi‐slice, echo planar acquisition, and approximately three‐ and six‐fold higher for three‐dimensional echo planar images acquired with isotropic resolutions of 0.7 and 0.55 mm, respectively. Improvements in parallel imaging performance (geometry factor) were up to around 1.5‐fold with increasing acceleration factor, and improvements in fMRI detectability (temporal signal‐to‐noise ratio) were up to around four‐fold depending on the distance to the coil. Although deeper lying structures may not benefit from the design, most fMRI questions pertain to the neocortex which lies within approximately 4 cm from the surface. These results suggest that the resolution of fMRI (at 7 T) can approximate levels that are closer to the spatial/temporal scale of the fundamental functional organization of the human cortex using a simple high‐density coil design for high sensitivity. Copyright © 2012 John Wiley & Sons, Ltd.     

Scanning-slit photon counting x-ray imaging system using a microchannel plate detector

An experimental prototype of a novel photon counting x-ray imaging system was evaluated. This system is based on an "edge-on" microchannel plate (MCP) detector and utilizes scanning slit imaging configuration. The detector is capable of photon counting, direct conversion, high spatial resolution, controllable physical charge amplification, quantum limited and scatter free operation. The detector provides a 60 mm wide field of view (FOV) and its count rate is 200 kHz for the entire FOV. The count rate of the current system is limited by the position encoding electronics, which has a single input for all events from the entire detector, and incorporates a single channel ADC with 1 micros conversion time. It is shown that the count rate can potentially be improved to clinically acceptable levels using multichannel application specific integrated circuit (ASIC) electronics and multi-slit image acquisition geometry. For a typical acquisition time used in this study, the image noise was measured to be less than the typically acceptable noise level for medical x-ray imaging. It is anticipated that the noise level will be also low after the implementation of the ASIC electronics. The quantum efficiency of the detector was measured to be 40%-56% for an energy range of 50-90 kVp for MCPs used in this study and can be improved to > 80% using MCPs with the optimized parameters. Images of resolution and anthropomorphic phantoms were acquired at an x-ray tube voltage of 50 kVp. The value of contrast transfer function for the detector was measured to be 0.5 at a spatial frequency of 5 lp/mm. The intrinsic spatial resolution of the system is 28 microm FWHM and was limited by the accuracy of the time-to-digital conversion of the position encoding electronics. Given the advantages of the edge-on MCP detector such as direct conversion and physical charge amplification, it can potentially be applied to mammography and chest radiography.     

Logarithmic amplifier for computed tomography tasks using fluoroscopic projections

The image intensifier (II)-based imaging systems, as radiotherapy simulators or C-arm X-ray units, have also been used for image acquisition in computed tomography. When analogue-to-digital conversion is performed on the output signal of the television camera, the accuracy for low-amplitude video signals, corresponding to X-ray pathways crossing high attenuation structures, is limited. To deal with this lack of accuracy, we investigated the benefits of using a logarithmic amplifier (LOGAMP) inserted between the television camera output and the analogue-to-digital converter (ADC) in the image acquisition chain. Such a device was intended to provide better use of the available ADCs of a given resolution and actually to reduce the quantization noise. Simulated data were used in this study, and cases with and without logarithmic amplifier were compared. Based on the simulation results, we formulate requirements for several signal and acquisition system parameters where the use of such a circuit is recommended.     

Logarithmic amplifier for computed tomography tasks using fluoroscopic projections

The image intensifier (II)-based imaging systems, as radiotherapy simulators or C-arm X-ray units, have also been used for image acquisition in computed tomography. When analogue-to-digital conversion is performed on the output signal of the television camera, the accuracy for low-amplitude video signals, corresponding to X-ray pathways crossing high attenuation structures, is limited. To deal with this lack of accuracy, we investigated the benefits of using a logarithmic amplifier (LOGAMP) inserted between the television camera output and the analogue-to-digital converter (ADC) in the image acquisition chain. Such a device was intended to provide better use of the available ADCs of a given resolution and actually to reduce the quantization noise. Simulated data were used in this study, and cases with and without logarithmic amplifier were compared. Based on the simulation results, we formulate requirements for several signal and acquisition system parameters where the use of such a circuit is recommended.