Effect of operational amplifier imperfections on single amplifier filters

A general method is given for the analysis of single amplifier RC-active filters using nonideal operational amplifiers (OA). It is shown that the output resistance of the OA has a significant effect in the passband and stopband in addition to the known deviations due to the finite gain—bandwidth product. The nonideal transfer functions in the factorized form, giving clearer concept of the effects of the nonideal OA, are obtained using some realistic approximations based on the typical specifications of modern general purpose OA. Expressions thus obtained closely follow the exact transfer functions, as demonstrated in the illustrative examples given, and their validity is confirmed by the experimental results.     

Synthesis of low-pass double-ladder operational amplifier network with prescribed pole sensitivities

This paper discusses the realization of low-pass filters having a pair of complex conjugate poles by a multiple feedback RC operational amplifier network. When the pole sensitivity with respect to the amplifier gain is prescribed, it is shown that the gain can be determined and then the synthesis proceeds in a way similar to the one with an infinite gain amplifier. This structure uses fewer passive elements as compared to Hakim's structure and the quadratic sensitivity index is closer to its theoretical minimum.     

Noise performance of operational amplifier circuits

A method for calculating the total noise voltage at the output of inverting and noninverting amplifiers modeled using one- and two-pole differential gain expressions for the operational amplifier is developed. This method is adapted to deal with the case of a low-pass filter stage constructed using an operational amplifier modeled by a one-pole differential gain expression. The results obtained are presented in tabular form for convenient analysis and provide a basis for producing amplifier designs with improved noise performance     

A new single operational amplifier active RC bandpass network with reduced sensitivity to amplifier gain-bandwidth product

A new configuration for realizing a low sensitivity active RC bandpass filter suitable for hybrid integrated realization is given. The network consists of a single operational amplifier (OA) and two identical passive RC bandpass building blocks. The active element sensitivities are given. The frequency limitation equations of the filter based on the one-pole rolloff model of the OA are derived. It is found that the choice of the element ratios of the passive RC networks plays an important role in the overall performance of the active resonator. Two cases are discussed in detail: one has the advantage of having better element ratios, and the other has the advantage of having lower sensitivities. The given network is less sensitive to the amplifier' gain-bandwidth product than other low sensitivity active RC bandpass networks using two operational amplifiers.     

运放对压电陶瓷驱动电路系统精度影响的研究

为了在光刻机投影物镜中使用压电陶瓷对像质补偿镜组进行精密定位,设计了一种以集成运算放大器构成的压电陶瓷驱动电路。针对光刻物镜中压电陶瓷的亚微米量级高精度定位要求,研究了驱动电路的系统精度要求,并对系统误差进行分解,着重分析了运算放大器放对系统精度的影响。首先,分析运放失调误差的影响;其次,使用PSpice仿真获得运放的固有频率特性,分析工作带宽下运放有限开环增益的影响;然后,对运放反馈网络的影响进行分析;最后,分析运放输出噪声的影响。计算表明,在最坏情况下该压电陶瓷驱动电路中由运算放大器引起的系统误差小于130mV,满足系统误差分配的要求。试制了系统样机并进行了验证实验,实验结果表明由运放引起的系统误差不超过100mV,与理论分析的结果符合。     

Generation and classification of single amplifier filters

A unified approach is presented for generating configurations for circuits containing one operational amplifier together with RC elements and capable of realizing a general second-order voltage transfer function. Systematic application of the generation procedure leads to various single amplifier biquads with the known circuits, as well as some new ones, obtained as special cases. The insight gained from the generalized approach as well as the results of a general sensitivity analysis (including the effects of the amplifier limited bandwidth) offer a method for categorizing and classifying single amplifier filters. The different filter classes are illustrated and compared with the aid of extensive design tables. General equations for the effect of the amplifier limited bandwidth are also given.     

Frequency-dependent OP-AMP gain influence on parameters of the single amplifier biquad filters

The influence of the finite gain and gain-bandwidth product of the operational amplifier on the parameters of the active RC filter has been investigated in the present paper. Single amplifier biquad filters were analysed for the case when the central frequency in the pole pair does not depend on the amplifier gain, i.e. when S = 0. The general results were obtained for such filters, describing well the filter behaviour at low as well as at high frequencies. On the basis of the results obtained, the deviation of the realized parameters from the desired values can be determined, and thereby the necessary correction of the filter calculation can be made. The experimental results agree well with the theoretical ones.     

新型功率运算放大器PA05及其在线性功率源中的应用

介绍一种新型的功率运算放大器PA05，首先介绍了PA05的特点，引脚功能及使用方法，然后介绍了PA05在线性电流源中的应用，给出了基于PA05的实用功率放大电路，分析了其工作原理。     

New sinusoidal oscillator configurations using operational transresistance amplifier

The objective of this brief is to introduce four new structures of electronically tunable sinusoidal oscillators (SOs) designed using operational transresistance amplifier (OTRA). Each of the proposed SO consists of forward path derived from a generic structure along with one/two OTRA-based resistive gain stages or differentiator in its feedback path. All the proposed SOs enjoy independent tuning of the frequency of oscillation (FO) through resistors without affecting the condition of oscillation (CO). Further, all topologies are found to exhibit low f_o sensitivities at all frequencies with respect to circuit parameters, and the second topology is capable of achieving very low frequencies (VLFs) using less RC component spread and provides linear tuning too. The fourth circuit provides quadrature output. The proposed SOs have been successfully implemented and verified in 180-nm CMOS technology node using ADE (analog design environment) tool Cadence Virtuoso. Both prelayout and postlayout simulation results have been included. To assess the oscillator prefabrication performances, Monte Carlo and process-voltage-temperature (PVT) analyses have been performed. The total harmonic distortion (THD) is observed to be less than 3.5%.     

Automatic measurement of frequency characteristics of operational amplifier circuits

Laboratory experiments were developed for measuring the frequency characteristics of operational amplifier circuits using a personal computer with a data acquisition unit. A periodic rectangular wave, which is easily generated by a DA (digital/analog) converter, is applied to the circuit: then the steady-state response is digitized by an AD converter. Filon's method was used for the numerical Fourier integration of the sampled response. The errors associated with the measurement of the frequency characteristics of an integrator were found to be less than 0.2 dB and 1 degrees in gain and phase, respectively, within the frequency range satisfying the condition that the gain be >or=0 dB.<>     

高频有源滤波器的实用设计

本文给出了高频有源滤波器的实用设计方法。根据给定的技术指标，首先设计一个基于运算放大器的RC有源原形滤波器，然后根据网络理论，将其转换成基于电流传输器（CCⅡ－）的RC有源滤波器。由于两个滤波器具有相同的传输函数以及相同的元件值，因此，基于CCⅡ－的滤波器保留了原形滤波器的优良性能。文中给出了用AD844实现的滤波器电路以及计算机模拟结果。     

Some fundamental properties of second-order active RC filters with composite operational amplifiers

Second-order active RC filters employing N identical operational amplifiers (OAs) are considered. the way to achieve the highest-order zero sensitivities of the dominant poles is shown. It leads to composite operational amplifiers (COAs) with a gain function of a polynomial form. the analysis of sensitivities, errors and location shifts of dominant poles as well as the effects of parasitic poles is also provided. the results have been confirmed by numerical analysis and an experimental verification.     

On the realization of current transfer function using voltage amplifiers

Current transfer function is a feature of current‐mode filters. Current‐mode filters have so far been realized principally using current amplifiers and current conveyors. Some current‐mode filter architecture using operational amplifiers have also been reported. In this article it is shown that by using the principles of transposed network and nullor model for the active device, a current transfer function can be realized in a very simple way using a voltage amplifier, i.e. operational amplifier (OA). The key concept is the knowledge that each ideal (i.e. infinite gain) controlled source is exactly equivalent to a nullor. Thus, a voltage‐mode filter implemented using an ideal three terminal (output, input and ground) OA can be very easily converted to a current‐mode filter using the same OA. The principle has been illustrated by considering single‐OA‐ and multi‐OA‐based second‐order voltage‐mode filters. SPICE simulation results are provided to validate the theoretical concept. Copyright © 2006 John Wiley & Sons, Ltd.     

High-gain,high-CMRR class AB operational transconductance amplifier based on the flipped voltage follower

A novel class AB operational transconductance amplifier (OTA) topology is proposed, based on a class AB flipped voltage follower. The OTA has class AB behavior, with current boosting both for the load and the compensation capacitors. It has a high gain of (g_mr₀)⁴ , obtained using a two-stage structure with cascoded stages, and is a two-stage Miller-compensated amplifier employing multipath to remove the positive zero. It has close to rail-to-rail output swing (limited by cascoding) and very low common-mode gain thanks to a replica technique (allowing the use of low-power common-mode feedback [CMFB] loops). Ninety-two decibels of gain and 176 dB of common-mode rejection ratio (CMRR) without CMFB are achieved using a 40-nm complementary metal-oxide semiconductor (CMOS) process. The OTA is used to design a low-power sample-and-hold amplifier (SHA) operating at 5 MSps, a typical application for CMOS OTAs, which has been chosen to verify the proposed circuit's performance and to show that the OTA is robust in Monte Carlo simulations under process variations and mismatches in an actual application.     

新型功率放大器

简要介绍了甲类和乙类功率放大器原理,分析了其优缺点;详细论述了采用高压运算放大器、跨导技术和甲乙类推挽电路技术所设计电子线路的工作原理;设计了高稳定性、低失真度、甲乙类全互补推挽式功率放大器.     

A comparative study of multiple amplifier active RC biquadratic sections

Biquadratic sections play an important role in the design of high order active filters. This paper compares a number of popular multiple amplifier active RC biquads on the basis of their sensitivities as well as ω₀ and Q enhancement effects due to finite amplifier gain–bandwidth products (GB). For sensitivity comparison, statistical sensitivity measures, which take into account the tolerances of various passive and active elements, are used. Simple expressions for gain, phase and transfer function sensitivities are derived for the case of uncorrelated element variations. Graphic illustrations of the effects of increasing ω₀ and Q on the sensitivity measures are presented. In addition, root-loci, which show the effects of GB on the network poles are included. To further facilitate the comparison, graphs demonstrating changes in ω₀ and Q due to GB are also presented.     

Micropower high current‐drive class AB CMOS current‐feedback operational amplifier

A novel CMOS current‐feedback operational amplifier (CFOA) aimed to low‐power applications is proposed. The use of a compact class AB implementation allows high current‐drive capability and simultaneously very low quiescent power consumption. Measurement results of a fabricated prototype show for an inverting configuration a closed‐loop bandwidth of 1 MHz independent of gain setting, and a slew rate of 2V/µs for a load capacitance of 30 pF and a quiescent power consumption of 264µW. Copyright © 2010 John Wiley & Sons, Ltd.     

Design of a 75‐nW, 0.5‐V subthreshold complementary metal–oxide–semiconductor operational amplifier

This work focuses on the subthreshold design of ultra low‐voltage low‐power operational amplifiers. A well‐defined procedure for the systematic design of subthreshold operational amplifiers (op‐amps) is introduced. The design of a 0.5‐V two‐stage Miller‐compensated amplifier fabricated with a 0.18‐µm complementary metal–oxide–semiconductor process is presented. The op‐amp operates with all transistors in subthreshold region and achieves a DC gain of 70 dB and a gain–bandwidth product of 18 kHz, dissipating just 75 nW. The active area of the chip is ≈0.057 mm². Experimental results demonstrate that well‐designed subthreshold op‐amps are a very attractive solution to implement sub‐1‐V energy‐efficient applications for modern portable electronic systems. A comparative analysis with low‐voltage, low‐power op‐amp designs available in the literature highlights that subthreshold op‐amps designed according to the proposed design procedure achieve a better trade‐off among speed, power, and load capacitance. Copyright © 2013 John Wiley & Sons, Ltd.     

基于运放开环频率特性的放大器幅频特性分析

在实验测试中发现同相放大器的幅频特性在通频带内略有峰值出现。本文基于运放二阶模型论述了同相放大器幅频特性出现峰值的原因,进而讨论了反馈系数对其幅频特性的影响。通过仿真分析同相放大器幅频特性,指出电路设计时反馈系数在允许的范围内应尽量小,以减少运放的二阶特性对放大器的影响,这对运用运放设计放大电路有很好的指导作用。     

基于OPA820宽带放大器的设计

设计了一种宽带放大器,采用高速运算放大器OPA820和低失真电流反馈运算放大器THS3091构成两级放大电路,在6 Hz～20 MHz的通频带中实现放大增益为43 dB,具有带内波动小,输出噪声低的特点.同时将单一的5 V电源通过TPS61087和MC34063A产生系统所需要的正负电源为放大器供电.放大器输出经过精密...