The operational amplifier in linear active networks

In this article the two-port characteristics, the gain stability, and the sensitivity of the nonideal operational amplifier are presented. A unified approach is taken to cover both the inverting and the noninverting modes of amplifier operation. Some of the sensitivity aspects pertaining to network synthesis using operational amplifiers are also discussed.     

Simple 2nd-order amplifier model for differential and common-mode gain

In this contribution, a simple 2nd-order model of an operational amplifier is presented. This model, which is based on the inclusion of both the first and second most dominant poles in expressions for the gain associated with the inverting and noninverting inputs to the amplifier, permits more detailed considerations of the effects of differential and common-mode gain characteristics on op. amp. circuits than is possible by using the single-dominant-pole model.     

实用运算放大器网络中的虚地性质

本文提出用一个理想电压控制电流源(VCCS)并接于嵌在一个倒相放大器电路中的实际运算放大器(OP.amp)输入端,虚地性质(VGP)可以扩展到使用的运算放大器单位增益带宽那样高的频率.文中给出用真正运算放大器的VCCS的实用电路.用互补变换法可得出非倒相放大电路图.     

Comment on `gain-sensitivity product-a figure of merit for hybrid-integrated filters using single operational amplifiers'

A highly useful figure of merit has been suggested by Moschytz (see abstr. B17344 of 1971) for hybrid integrated circuits using a single operational amplifier for a multiloop active network. This figure of merit is shown to apply strictly only to single- loop active filters, whose closed-loop gain at the undamped natural frequency equals the inverse of the feedback path attenuation, due to the network. A generalized definition is given, which extends its usefulness to all kinds of single- and multiloop active filters, without any such restrictions.     

A grounded capacitor high-Q inductance simulator for tuned circuits applications

An operational amplifier (OA) RC realization of a high-Q inductor is presented. The circuit uses two OA's in unity gain connections, two grounded condensers, and three resistors. It is characterized by low sensitivity and good high-frequency performance. The active inductor, being open-circuit unstable, is suitable for tuned circuit and oscillator applications.     

Improving the bandwidth gain-independence and accuracy of the current feedback amplifier

A high-performance current feedback amplifier circuit referred to as an operational current feedback amplifier is described in this paper. The technique employed involves the incorporation of the input circuit of the current feedback amplifier in the feedback loop of an operational amplifier to reduce the input impedance at the inverting terminal of the current feedback amplifier. The new circuit possesses the gain accuracy and bandwidth of the current feedback amplifier but realizes significant improvement in bandwidth accuracy and bandwidth gain-independence. Experimentally, using AD844s, an order of magnitude reduction in bandwidth variation with changing gain was achieved in the noninverting configuration and almost complete bandwidth invariance was realized in the inverting configuration.     

RC active allpass sections

Two active networks are presented which are suitable for the realisation of a second-order allpass function. Each uses one differential-input operational amplifier and RC networks. The realisation is achieved to within a constant multiplier always smaller than unity.     

RC active network synthesis using an amplifier†

A new RC active network synthesis procedure for realizing a given open-circuit voltage transfer function is presented. The interconnection of an ideal voltage amplifier of gain greater than unity and two RC sub-networks in a grounded 2-port configuration is considered for this purpose. It is shown that a general rational transfer function of any order can be realized by such a configuration, provided the transfer function does not have zeros on the positive real axis of the s plane. The method compares favourably with other active RC synthesis procedures using a single finite-gain amplifier.     

Transfer function synthesis using a finite-gain amplifier

An active RC circuit employing a single finite–gain amplifier, one two–port and two ono–ports, has been presented here for the realization of n general voltage transfer function without positive real axis zeros. The comparative merits of the scheme with respect to that proposed by Rao (1969) are that the synthesis procedure is simpler and the number of passive circuit elements required is smaller. The coefficient of realization of the synthesized transfer function can always be made equal to unity with the scheme. A few examples are included to illustrate the synthesis procedure.     

State-Variable Synthesis for Insensitive Integrated Circuit Transfer Functions

Using state-variable flow graphs and simple operational configurations suitable for integration, a theory for insensitive transfer function realization in terms of integrated circuits is discussed. The theory emphasizes the decomposition into second-order systems that are developed, following state-space concepts, with special reference to their sensitivity which is shown to be very low for high operational amplifier gains.     

Novel chaotic oscillator configuration using a diode-inductor composite

A general sinusoidal oscillator configuration is designed and then modified for chaos using a second-order nonlinear grounded diode-inductor composite. The configuration has an operating frequency that can be electronically tuned by varying the gain of an inverting amplifier stage. In addition to this amplifier, a single positive-type second generation current conveyor (CCII+), two noninverting integrators and two grounded resistors are required. The case where one of the integrators is replaced with an all-pass filter is investigated. Since the configuration is designed at a functional level, different circuit realizations are possible. Experimental results and PSpice simulations of a constructed implementation based on current feedback op amps are included. Numerical simulations of the derived chaotic mathematical models using a piecewise linear approximation of the diode current-voltage characteristics are also shown.     

Large bandwidth BiCMOS operational amplifiers for SC videoapplications

A single-ended and a fully differential broadband BiCMOS operational amplifier for switched-capacitor video applications are presented. The amplifiers feature a folded cascode gain stage with a current source as output load. For the single-ended amplifier the current mirroring is accomplished with a modified bipolar Wilson current mirror at the output of the differential pair. Symbolic expressions for the transfer functions for both amplifiers are derived. The amplifiers are integrated in an analog 1 μm BiCMOS process with an active die area of 0.72 mm² and 0.96 mm² for the single-ended and the fully differential amplifier, respectively. For both amplifiers a DC-gain of 68 dB and a unity gain frequency greater than 250 MHz was measured for a power supply voltage of 5 V     

On a new topology for the transconductance feedback amplifier

A new topology for a transconductance feedback amplifier (TFA) is presented in this paper. The topology offers the advantage that it is capable of realizing the negative of the standard inverting gain expression. That is, gains of the form +R/sub 2//R/sub 1/. We will also show that it can realize the standard inverting and noninverting gains, all the while maintaining near constant bandwidth in each configuration as gain is varied. This first feature makes the proposed topology attractive for filtering applications since the TFA can function as an integrator, thereby allowing this amplifier to realize positive and negative lossless integrators. The proposed amplifier can also generate the logarithm of an input in the first and fourth quadrants, unlike previous TFA configurations. The proposed amplifier was verified experimentally for different gain configurations, integration and logarithmic capabilities by a chip designed using TSMC's 0.18-/spl mu/m CMOS process of a single ended power supply of 1.8 V. The chip occupied an area of 752.6 /spl mu/m by 581.2 /spl mu/m and contained the proposed amplifier and a conventional TFA for comparison purposes. A bandwidth of 15 MHz was observed for the proposed TFA in the unity gain (/spl plusmn/1) configuration.     

一种含理想运算放大器电路的讨论

为进一步明确含理想运算放大电路的有关概念和运算放大器的特性,本文从计算机仿真和理论分析两个方面,对一个含理想运算放大器电路的输入输出特性进行了模拟和推导.结果表明该电路在线性输入范围内是一电压跟随器,若超出线性输入范围,则输出波形严重失真;带反馈电路与开环电路相比较表现为线性输入范围扩大、电压增益减小,而这正是电路负反馈的特性.因此,不能简单的把接在运算放大器同相输入端的反馈视为正反馈.     

Flexible active filter design using operational amplifier pole

A synthesis procedure for generating second-order active filters using the operational amplifier pole and a single external capacitor is given. The proposed method is based on drawing the signal-flow graph from the given transfer function and obtaining the circuit realization from the graph.     

采用输入信号适配技术的BiCMOS运放

为了满足高性能开关电源中集成运放的应用需要,设计了一种结构简单且具有轨对轨输出的运算放大器.该运放基于0.5μm BiCMOS 工艺,采用浮动输出的输入信号适配器(ISAFO),将输入信号放大至差分输入级的工作区域,从而实现了轨对轨的运行.对所设计的运放进行了仿真分析,结果表明在工作电源电压为±0.75 V、外接100 kΩ电阻的条件下,该运放的直流开环增益达到了102 dB,单位增益-带宽为6.35 MHz,相位裕度为62.5°,而功耗仅约为150 μW.所设计的运放具有很宽的共模输入范围及较高的增益,所以特别适用于开关电源的误差放大器、过流、过压和过热保护模块中.     

A precision bipolar current-differencing amplifier

A temperature-stable wide-band current-differencing amplifier resulting from the replacement of the usual operational amplifier structures by integrable current-operated modules is reported. This unity gain network features nearly ideal terminal characteristics (R/SUB IN/<0.3 /spl Omega/, R/SUB OUT/ /spl esdot/ 2 M/spl Omega/) and an external adjustment to maximize the subtraction accuracy, or current gain common mode rejection ratio.     

一种带增益提高技术的高增益CMOS运算放大器的设计

给出了一种用在高速高精度流水线型模数转换器中的具有高增益和高单位增益频率的全差动CMOS运算放大器的设计,电路结构主要采用折叠式共源共栅结构,并采用增益提高技术提高放大器的增益。共模反馈电路由开关电容共模反馈电路实现。模拟结果显示,其开环直流增益可达到106 dB,在负载电容为2 pF时单位增益频率达到了167 MHz,满足了对模数转换器的高速度和高精度的要求。     

A feedforward excess-phase cancellation technique for integrators

Integrators are useful analogue function blocks. A representative application of integrators is a continuous-time filter on an integrated circuit. Excess phase shift of integrators is one of the most severe problems, because excess phase shift at the unity gain frequency degrades the frequency characteristics of the filters. This paper describes a feedforward excess-phase cancellation technique. The proposed technique is applied to integrators which have feedback with an amplifier. The proposed idea is verified by experiment. It is shown that the excess-phase shift due to the gain-bandwidth product of operational amplifiers is cancelled. The proposed technique is useful for realization of integrated continuous-time filters using integrators because extra capacitors are unnecessary. An integrator with the excess-phase cancellation and a third-order leapfrog filter using the integrator are designed and demonstrated by HSPICE simulation. The integrator has a parasitic pole whose frequency is proportional to the unity gain frequency. The simulation results show that the phase characteristics are improved by the proposed technique over the wide range of the unity gain frequency.     

高性能折叠式共源共栅运算放大器的设计

折叠式共源共栅结构能够提供足够高的增益,并且能够增大带宽、提高共模抑制比和电源电压抑制比.基于Chartered 0.35 μm工艺,设计了一种折叠式共源共栅结构的差分输入运算放大器,给出了整个电路结构.Spectre仿真结果表明,该电路在3.3V电源电压下直流开环增益为121.5dB、单位增益带宽为12 MHz、相位裕度为61.4°、共模抑制比为130.1dB、电源电压抑制比为105 dB,达到了预期的设计目标.