两级电平结构MRI梯度放大器的研究

梯度放大器是核磁共振成像(MagneticResonanceImaging,简称MRI)系统中的重要设备。本文根据一套MRI梯度系统所需的性能指标设计了一种两级电平结构的梯度放大器,并对其结构进行了仿真和实验研究。仿真结果和实验验证均表明,这种两级电平结构适合实现MRI梯度系统需要的高精度梯形波电流,采用的改进型PWM策略能有效地降低稳态电流的纹波。     

JF—12F放大器功率级的故障和解决办法

在XWD_1系列小型电子电位差计以及XDD_1电子平衡电桥(总称电子自动平衡显示仪表)中采用的JF—12F型放大器功率级,经常遇到3CG14(或3CG15)两只晶体管烧坏以及3AD_6两只大功率晶体管发烫(长期运行管壳温度可达70℃以上)等问题,这对仪表的安全运行、使用寿命都带来影响,也给仪表检修工人增添了工作量。通过理论计算和实践,我们发现这主要是JF—12F型放大器功率级电路参数设置不合理而导致的。图1为JF—12F型放大器功率级电路图。由于电路上、下对称并且电路工作大都在平衡状态,所以可化简为如图2等效电路。     

基于AD603程控增益大功率宽带直流放大器的设计

采用低噪声增益可程控集成运算放大器AD603和高频三极管2N2219和2N2905等器件设计了宽带直流放大器,该放大器具有增益可程控、功率高、频带宽、带宽可选择等特点。输入级采用两级AD603级联,以提高增益控制范围;中间级采用分立元件制作了高输出功率放大器,输出级设计了两路通频带分别为0～5MHz以及0～10MHz的低通滤波器实现带宽的可预置,通过51单片机可以对放大器增益和带宽进行控制。此外对提高直流放大器的各种性能指标提出了多种具体措施,在自动化要求较高的系统中具有很好的实用性。     

流量变送器的快捷检查法

涡轮流量变送器的作用是把流量转变为电信号,经放大后送到流量指示、累积仪表处理,放大器安装在壳体上部,两者之间通过螺纹连接。放大器的电原理如附图所示,它由四级组成,前两级是电压放大,后两级是发射极组合输出。     

超线性放大器及其胆管的应用与代换

胆管,即为电子管,其组成的末级放大器有三极管接法、五极管接法、超线性接法等三种类型。哪一种接法能够胜任数字音频技术发展的潮流呢?显然是超线性放大器具有推波助澜之优势。下面着重向读者介绍一款超线性放大器及其胆管的应用及代换。一、超线性放大器的接法所谓放大器末级接法处于何种状态,关键取决于     

半导体多级放大器

在工程实际测量中,被测信号往往非常微弱,因此要达到正确测量和控制的目的,应使被测信号经过多级放大器放大。在多级放大器中,根据各级所处位置和用途不同,可分为四个部分:输入级、中间级、末前级和末级。其中前几级通常是为了获得一定的电流或电压增益,使微弱的原始信号得到需要的放大,以满足末级——功率放大级输入的要求。多级放大器的末级一般为功率放大器,其目的是为了得到一定的输出功率以控制执行机构。     

基于OPA454的新型高压级联放大器优化设计

为获取频率可调的高线性度电压信号,提出基于OPA454的高压级联线性放大器的优化设计方案。首先,设计高压级联放大器的主电路、隔离电路和级联放大电路;然后,分析此线性放大器的负反馈特性和容性负载特性,保证输出电压信号的高线性度和带容性负载能力;最后,搭建两级级联放大电路模型,时域下测试输入电压频率分别为0.001 Hz、1.0 Hz、1.0 kHz、10 kHz时放大器的输入输出波形,在频域下对比一级电压放大电路和两级电压放大电路的频率响应曲线。结果表明:设计的新型线性放大器输出的电压波形可对输入电压线性放大40 n倍,并达到较高的线性度和低波形失真率,满足可调频率下电压准确放大的要求。     

前馈技术

一个运算放大器的性能,可用前馈技术来加以改进。这种前馈法的基本原理是:让信号的高频段经过一个提升放大器,来绕开该运算放大器的前面几级,以扩展频带宽度。其基本线路如图1所示。有些运算放大器是具备引入前馈技术的条件的。其实,只要运算放大器的末级输入也能从外部引入即可。     

高频小信号双参差调谐放大器电路分析与特性仿真研究

高频小信号调谐放大器是电子装备中的常用电路,为了拓宽通频带、改善选择性,实际中常采用双参差调谐放大器。双参差调谐放大器中两级级联的单调谐放大器电路结构相同、谐振频率不同,合理地选择单调谐放大器电路选频网络的电路参数,可使双参差调谐放大器电路具有宽单峰特性或双峰频率特性,实现较宽的通频带和较好的选择性。借助Multisim仿真软件可对电路结构和参数进行设计优化。     

L15前置分配混合放大器原理与检修

L15录像机没有给出前置分配混合放大器的资料,给广大维修工作者增添了困难。本文弥补了原资料的不足,不仅给出了放大器的电路,还分析了原理及常见故障和检修办法。前置分配混合放大器是L15录像机高频系统的一组件,包括输入回路,一级RF放大器,分配器,二级RF放大器,混合器等五部分,如图1所示,它主要为录像机调潜器和电视机提供放大的电视信号。从图1看出,天线来的电视信号,经输入回路,一级RF放大器,二分配器后分作两路:一路送至录像机调潜器,供记录用;另一路经二级RF放大器,混合器后,从射频插座输出。使得录像机在录制一套节目的同     

DC analysis and design of a PWM buck converter operated as a dynamic power supply

Modern energy transmission and signal reproduction techniques rely upon power amplifiers that must operate with high efficiency. An increasingly popular technique for addressing this problem involves replacing the fixed power amplifier supply voltage V _{D D} with a controlled, variable voltage provided by a dynamic power supply. Although pulse‐width modulated dc‐dc buck converters typically function as fixed‐output supplies, this paper provides new theoretical dc analysis for operation wherein the output voltage is controlled and continuously variable over a wide range. A design procedure for the variable‐output buck converter is derived. Key device parameters affecting converter speed and efficiency are identified. The dc analysis and design procedure are verified experimentally, with calculated and measured parameters shown to be in good agreement. Copyright © 2016 John Wiley & Sons, Ltd.     

Introduction to the Special Issue on Smart Power Device Reliability

This Special topic Issue of IEEE TRANSACTIONS ON DEVICE AND MATERIALS RELIABILITY documents the recent progress in the area of reliability of Smart Power devices. These high voltage/power devices such as LDMOS and DeMOS are increasingly integrated into advanced process technologies for mixed signal IC applications, e.g. smart low-side and high-side drivers, motor and relay driver/controllers, printer and display drivers/controllers, audio amplifiers, xDSL line drivers, high efficiency power management circuits for ac/dc conversion and dc/dc conversion (programmable buck, boost, and linear regulators). Reliability challenges in these devices are gaining more attention in the industry. This issue contains one review paper and several contributed papers covering a range of topics on reliability physics, characterization, and failure mechanisms of Smart Power devices. This collection of articles will be of great interest to anyone working in the held of Smart Power reliability     

Wide bandgap semiconductor transistors for microwave poweramplifiers

Explores the RF power performance of microwave amplifiers fabricated from wide bandgap semiconductor transistors and demonstrates that microwave power amplifiers fabricated from 4H-SiC and AlGaN/GaN transistors offer superior RF power performance, particularly at elevated temperatures. Theoretical models predict room temperature RF output power on the order of 4-6 W/mm and 10-12 W/mm, with power-added efficiency (PAE) approaching the ideal values for class A and B operation, available from 4H-SiC MESFETs and AlGaN/GaN HFETs, respectively. All calculations were thoroughly calibrated against dc and RF experimental data. The simulations indicate operation at elevated temperature at least up to 5000°C is possible. The RF output power capability of these devices compares very favorably with the 1 W/mm available from GaAs MESFETs. The wide bandgap semiconductor devices will find application in power amplifiers for base station transmitters for wireless telephone systems, HDTV transmitters, power modules for phased-array radars, and other applications. The devices are particularly attractive for applications that require operation at elevated temperature     

Impact of MOSFET Gate-Oxide Reliability on CMOS Operational Amplifier in a 130-nm Low-Voltage Process

The effect of the MOSFET gate-oxide reliability on operational amplifier is investigated with the two-stage and folded-cascode structures in a 130-nm low-voltage CMOS process. The test operation conditions include unity-gain buffer (close-loop) and comparator (open-loop) configurations under the dc stress, ac stress with dc offset, and large-signal transition stress. After overstress, the small-signal parameters, such as small-signal gain, unity-gain frequency, and phase margin, are measured to verify the impact of gate-oxide reliability on circuit performances of the operational amplifier. The gate-oxide reliability in the operational amplifier can be improved by the stacked configuration under small-signal input and output application. The impact of soft and hard gate-oxide breakdowns on operational amplifiers with two-stage and folded-cascode structures has been analyzed and discussed. The hard breakdown has more serious impact on the operational amplifier.     

Single Miller capacitor frequency compensation with nulling resistor for three‐stage amplifiers

A frequency compensation technique for three‐stage amplifiers is introduced. The proposed solution exploits only one Miller capacitor and a resistor in the compensation network. The straightness of the technique is used to design, using a standard CMOS 0.35‐µm process, a 1.5‐V OTA driving a 150‐pF load capacitor. The dc consumption is about 14µA at DC and a 1.8‐MHz gain–bandwidth product is obtained, providing significant improvement in both (MHzpF)/mA and ((V/µs)pF)/mA performance parameters. Copyright © 2007 John Wiley & Sons, Ltd.     

Linearization: reducing distortion in power amplifiers

This article discusses techniques for the cancellation of distortion (linearization) in power amplifiers. Different methods of linearization are introduced and compared. The linearization of solid-state power amplifiers (SSPAs), traveling-wave tube amplifiers (TWTAs) and klystron power amplifiers (KPAs) are considered. Although the focus of this article is on power amplifiers, many of the techniques are applicable to other components such as mixers, low-noise amplifiers, and even photonic components, such as lasers and optical modulators     

可重构连续型 F 类超宽带功率放大器

带宽与效率是功放设计中的两项重要指标,如何使功放同时满足宽频带、高效率的设计要求一直是功放研究的热点和难点之一。本文基于硬件智能化技术和连续理论提出了连续型F类超宽带功率放大器,以连续理论扩大阻抗匹配空间,将传统F类功放推广至连续型F类功放,有效拓宽其工作带宽,并以可重构技术将分散的频段整合为整体。通过测试,该功放在0.9～4 GHz范围内,功率附加效率(power added efficiency, PAE)大于72%,增益约为12.5 dB,饱和输出功率为41 dBm。本设计将可重构技术和连续理论二者优势结合,具有宽频带、高效率、智能性等优点,能够很好地适应5G无线通信系统的需求。     

Ultrabroad-band Raman amplifiers pumped and gain-equalized bywavelength-division-multiplexed high-power laser diodes

This paper reviews recent progress in broad-band Raman amplifiers for wavelength-division-multiplexed (WDM) applications. After the fundamentals of Raman amplifiers are discussed in contrast to erbium-doped fiber amplifiers, a new technique called “WDM pumping” is introduced to obtain ultrabroad and flat gain in Raman amplifiers only using WDM diode pumps. The design issues of this technique are then developed to realize outstanding performances such as 100 nm of flat gain bandwidth, 0.1 dB flatness over 80 nm, and so forth     

Simplified analysis of feedback amplifiers

A very simple and general method for the analysis of feedback amplifiers with large-loop gain is presented in this paper. The general properties of feedback amplifiers, such as gain and input and output resistances, are obtained using an open-loop circuit where the loading effect of the feedback network is easily taken into account. Emphasis is placed on quick, intuitive, and reliable calculations, useful for both the analysis and design of feedback amplifiers.     

Fiber-based optical parametric amplifiers and their applications

An applications-oriented review of optical parametric amplifiers in fiber communications is presented. The emphasis is on parametric amplifiers in general and single pumped parametric amplifiers in particular. While a theoretical framework based on highly efficient four-photon mixing is provided, the focus is on the intriguing applications enabled by the parametric gain, such as all-optical signal sampling, time-demultiplexing, pulse generation, and wavelength conversion. As these amplifiers offer high gain and low noise at arbitrary wavelengths with proper fiber design and pump wavelength allocation, they are also candidate enablers to increase overall wavelength-division-multiplexing system capacities similar to the more well-known Raman amplifiers. Similarities and distinctions between Raman and parametric amplifiers are also addressed. Since the first fiber-based parametric amplifier experiments providing net continuous-wave gain in the for the optical fiber communication applications interesting 1.5-μm region were only conducted about two years ago, there is reason to believe that substantial progress may be made in the future, perhaps involving "holey fibers" to further enhance the nonlinearity and thus the gain. This together with the emergence of practical and inexpensive high-power pump lasers may in many cases prove fiber-based parametric amplifiers to be a desired implementation in optical communication systems