高频宽增益小信号放大器的设计及在医用超声功率计中的应用

介绍供医用超声功率计用的两种高频、宽增益的小信号放大器，并比较了它们彼此的优缺点。     

Two-electrode non-differential biopotential amplifier

A circuit is proposed for a non-differential two-electrode biopotential amplifier, with a current source and a transimpedance amplifier as a potential equaliser for its inputs, fully emulating a differential amplifier. The principle of operation is that the current in the input of the transimpedance amplifier is sensed and made to flow with the same value in the other input. The circuit has a simple structure and uses a small number of components. The current source maintains balanced common-mode interference currents, thus ensuring high signal input impedance. In addition, these currents can be tolerated up to more than 10μA per input, at a supply voltage of ±5V. A two-electrode differential amplifier with 2×10 MΩ input resistances to the reference point allows less than 0.5μA per input. The circuit can be useful in cases of biosignal acquisition by portable instruments, using low supply voltages, from subjects in areas of high electromagnetic fields. Examples include biosignal recordings in electric power stations and electrically powered locomotives, where traditionally designed input amplifier stages can be saturated.     

Microelectrode amplifier with improved method of input-capacitance neutralisation

A circuit is described which allows the input capacitance of an f.e.t. input integrated circuit to be used both as the feedback capacitance to neutralise the total input capacitance and to inject current pulses into the input. Compared with the conventional method of adding discrete capacitors to perform these functions, this design results in a lower total capacitance at the input, which reduces the high-frequency noise generated by the amplifier and facilitates the achievement of a low effective capacitance. A modified version having an ultralow (0·1pA) input current, for use with ion-sensitive microelectrodes, is also described.     

Simple two-electrode biosignal amplifier

A simple, cost effective circuit for a two-electrode non-differential biopotential amplifier is proposed. It uses a ‘virtual ground’ transimpedance amplifier and a parallel RC network for input common mode current equalisation, while the signal input impedance preserves its high value. With this innovative interface circuit, a simple non-inverting amplifier fully emulates high CMRR differential. The amplifier equivalent CMRR (typical range from 70–100 dB) is equal to the open loop gain of the operational amplifier used in the transimpedance interface stage. The circuit has very simple structure and utilises a small number of popular components. The amplifier is intended for use in various two-electrode applications, such as Holter-type monitors, defibrillators, ECG monitors, biotelemetry devices etc.     

Acoustical modulation of electrically evoked otoacoustic emission in intact gerbil cochlea

In order to study the interaction between mechanical-electrical and electrical-mechanical transductions of outer hair cells (OHCs) in vivo, we observed the acoustically induced changes in the electrically evoked otoacoustic emission (EEOAE). One pole of a bipolar electrode was placed in the round window niche and the other pole on the surface of the first cochlear turn in the gerbil. A microphone and a speaker were used to monitor the EEOAE and to deliver an acoustical tone, respectively. It was found that a high sound level acoustical tone enhanced the EEOAE fine structure at frequencies below the acoustical frequency, and suppressed the overall level of the EEOAE at frequencies above the acoustical frequency. In addition, the EEOAE at frequencies approximately one half octave lower than the acoustical frequencies were relatively more enhanced or showed relatively less suppression than at other frequencies. The amplitudes of these changes had a positive relationship with acoustical tone levels. Furosemide eliminated the acoustically caused EEOAE change indicating that the acoustically caused change in the EEOAE is a phenomenon of the normal cochlea. One possible mechanism for the results is that the electrically and acoustically evoked basilar membrane (BM) vibrations interact at the EEOAE generation site and change the local mechanical and electrical properties. The second possible mechanism is that the acoustical stimulus creates an impedance discontinuity at its characteristic frequency location leading to a change in the reflected electrically evoked traveling wave, which may enhance or suppress the EEOAE by the vector summation of two waves.     

新型4通道单电源低功耗程控接口脑电放大器的研制

本脑电放大器针对现有同类电路缺点进行改进，采用了最新一代高性能模拟与混合信号集成电路芯片，优化了电路结构并通过精细的电路工艺措施实现了噪声电压1．9μVp-p、共模抑制比100dB、输入阻抗80MΩ、基线漂移小、单电源5V供电和工作电流小于10mA等电路指标，并实现了增益控制和滤波控制的数字化接口。1年的应用表明该放大器安全省电、体积小、结构简单、性能稳定，非常适合作为便携式智能型脑电图仪器的前端。     

PA系列高压功率放大器在医学仪器设计和应用中须注意的问题

以PA08和PA84的实际应用为例,阐述了PA系列高压功率放大器在设计和应用中应注意的问题,着重探讨了放大器在医学仪器输出级的应用中的电源旁路和过压保护、电流限制、输出保护、放大器的安装和机械考虑等几个重点问题。     

Wireless amplified NMR detector for improved visibility of image contrast in heterogeneous lesions

To demonstrate the capability of a wireless amplified NMR detector (WAND) to improve the visibility of lesion heterogeneity without the use of exogenous contrast agents, a cylindrically symmetric WAND was constructed to sensitively detect and simultaneously amplify MR signals emitted from adjacent tissues. Based on a two‐leg high‐pass birdcage coil design, this WAND could be activated by a pumping field aligned along the main field (B₀), without perturbing MR signal reception. Compared with an equivalent pair of external detectors, the WAND could achieve more than 10‐fold gain for immediately adjacent regions. Even for regions with 3.4 radius distance separation from the detector's cylindrical center, the WAND was at least 1.4 times more sensitive than an equivalent pair of surface arrays or at least twice as sensitive as a single‐sided external surface detector. When the WAND was inserted into a rat's rectum to observe adjacent tumors implanted beneath the mucosa, it could enhance the detection sensitivity of lesion regions, and thus enlarge the observable signal difference between heterogeneous tissues and clearly identify lesion boundaries as continuous lines in the intensity gradient profile. Hyperintense regions observable by the WAND existed due to higher levels of blood supply, which was indicated by a similar pattern of signal enhancement after contrast agent administration. By better observing the endogenous signal contrast, the endoluminal WAND could characterize lesions without the use of exogenous contrast agents, and thus reduce contrast‐induced toxicity.     

Phase III results with a totally implantable piezoelectric middle ear implant: Speech audiometry,spatial hearing and psychosocial adjustment

Objective To evaluate the treatment efficacy of an electromechanical middle ear amplifier implant (AI) in patients with chronic moderate-to-severe sensorineural hearing loss (SNHL). The AI is a piezoelectric system with a sound processor and a rechargeable battery within a hermetically sealed titanium canister. Its titanium-sealed microphone is placed in the bony region of the ear canal. The incus-coupled transducer (actuator), which is also inside a titanium casing, is fastened to the adjacent bone.

Material and Methods This was a phase III study comprising 20 intention-to-treat patients. Telemetrical adjustments followed electromechanical amplifier implantations. We used a word recognition test as our primary efficacy measure (Freiburg Speech Recognition Test; DIN 45621). Secondary efficacy measures were the sentence comprehension test (Goettinger Satztest, 1996) for auditory orientation within noisy and quiet environments and a psychosocial adjustment test (Gothenburg Profile Test, 1998). The 6-month follow-up comprised a complete medical examination. Nineteen patients completed the study (per-protocol patients; 100% reference).

Results Seventeen patients (89%) demonstrated improved binaural recognition of phonetically balanced monosyllables. Fourteen postoperative patients (74%) attained a perfect score (100%) on this test, compared to only 3 preoperative patients (16%). Thirteen patients (68%) reached the sentence recognition threshold at a 2:1 dB signal-to-noise ratio during noisy trials. Correct identification of the noise source direction in the horizontal plane occurred in 89% of the trials. The Gothenburg Profile Test scores showed that the subjective evaluation of hearing, orientation, social behavior and self-confidence increased from 48% to 88%. Three patients did not benefit from the implant.

Conclusion Treatment of SNHL with a totally implantable hearing system can be an efficient method for those patients unable to wear hearing aids. However, in order to avoid implantation in non-responders, there is a need for more specific audiological indication criteria.     

一种用于神经刺激研究的触屏控制小型超声发生器

超声发生器是研究超声刺激的重要工具,但是目前并无可供选择的专用设备。目前实验室所用超声发生器通常都用多台通用仪器搭建而成,体积大,操作复杂。本文设计了一种用于神经刺激研究的小型超声发生器,用触屏作为控制界面,方便刺激参数的输入和修改;独立的E类末级功放非常小巧,可接近换能器放置,换能器的电抗参数纳入功放从而省去了匹配电路,整机体积进一步缩小。内置的现场可编程门阵列（FPGA）产生脉冲方波,经专门的驱动电路后控制E类功放中MOSFET的通断。测试表明,本文设计的超声发生器产生的波形准确,最高频率可达2 MHz。配接自制的500 kHz换能器,在30 V电源电压下输出功率6.23 W,最大声压达到168.3 kPa,并且还有可提升的空间。该发生器体积小,操作方便,电路设计简单,适用于超声神经刺激的研究。