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摘 要
运算放大器是电子电路中的基本模块，在家电，工业，国防军事以及科技电子仪器等领域有着广泛的应用。运算放大器(简称运放)因其早期应用在加减，积分，微分运算电路中而得名。运算放大器不仅可以对信号进行运算处理，也是有源滤波器，振荡器，以及各种比较器的重要组成部分。根据不同的需要，对运算放大器的设计提出了不同的要求。运算放大器具有非常高的电压增益，一般采用差分输入，有同相输入和正向输入两个输入端，采用单端输出和双端输出两种不同的输出形式。运算放大器在电路中一般采用闭环连接方式，形成负反馈网络，以减小非线性失真，展宽频带。单级运算放大器一般是稳定的，而多级运算放大器的频率特性较为复杂，需要进行频率补偿以保持其在闭环工作下的稳定性。
本论文以传统的两级运算放大器为例，阐述了放大器的频率补偿原理，介绍了几种多级运算放大器的频率补偿结构。基于Winbond0.5um的工艺设计了一种二级运算放大器，在提供较大直流增益的同时，增加了输入输出摆幅。采用了合适的频率补偿结构对其进行补偿，仿真结果表明，本文所设计的三级运算放大器在3.3v电源电压下，负载为5pf电容时，直流开环增益为155dB，单位增益带宽达到了32MHz，相位裕度为56.09°，具有较理想的频率响应和瞬态响应，并且所需的补偿电容值较小，优化了芯片的面积，较容易在CMOS工艺下实现。增益和相位裕度均满足设计要求。
关键词:多级运算放大器;频率补偿;相位裕度;稳定性
Abstract
Operational amplifier is the basic module of electronic circuits, and has a wide range of applications in the field of home appliances, industry, national defense, military and technology and electronic equipment. The operational amplifier (OP AMP) because of its early application in addition and subtraction, integral, differential operation circuit named. The operational amplifier can not only deal with the signal, but also is an important part of the active power filter, the oscillator and the comparator. According to different needs, the design of operational amplifier is put forward different requirements. The operational amplifier has a very high voltage gain, generally using differential input, there are two input terminals of the same phase input and forward input, and two kinds of different output forms. In the circuit, the a negative feedback network to reduce the nonlinear distortion. Single stage operational amplifiers are generally stable, amplifiers are more complex, so the frequency compensation is needed to keep the stability of the amplifier in the closed loop operation.
Taking the traditional two stage operational amplifier as an example, this paper expounds the frequency compensation principle of the amplifier, and introduces the frequency compensation structure. Based on O.I8} m, a three stage operational amplifier is designed in SMIC process, which increases the input and output swing at the same time with a larger DC gain. Using the appropriate frequency compensation structure, the compensation, simulation results show that, the design of three-stage operational amplifier in a supply voltage of 3.3V, load 5pf capacitor when the DC open loop gain for the 155dB, unity gain bandwidth to 32mhz, phase margin degree 56.09 0, with ideal frequency response and transient response, and the compensation capacitor value is smaller, optimize the chip area, easily implemented in CMOS technology. Gain and phase margin all meet the design requirements.
KEY WORDS:multistage operational amplifer; frequency compensation; phase margin; stability
目 录
2.3.3折叠式共源共栅(Folded-cascode)放大器9
