运算放大器

运算放大器

调节和放大模拟信号,它是用途十分广泛的器件,接入适当的反馈网络,可用作精密的交流和直流放大器、有源滤波器滤波器的供应商、振荡器振荡器的供应商及电压比较器比较器 的供应商。其应用领域已经延伸到汽车电子、通信、消费等各个领域,并将在未来技术方面扮演重要角色。

运算放大器的分类

运算放大器按参数可分为如下几类:

通用型运算放大器:主要特点是价格低廉、产品量大面广,其性能指标能适合于一般性使用。

低温漂型运算放大器:在精密仪器、弱信号检测等自动控制仪表中,总是希望运算放大器的失调电压要小且不随温度的变化而变化。

高阻型运算放大器:特点是差模输入阻抗非常高,输入偏置电流非常小,一般rid>1GΩ~1TΩ,IB为几皮安到几十皮安。

高速型运算放大器:主要特点是具有高的转换速率和宽的频率响应。

低功耗型运算放大器:由于电子电路集成化的最大优点是能使复杂电路小型轻便,所以随着便携式仪器应用范围的扩大,必须使用低电源电压供电、低功率消耗的运算放大器相适用。

高压大功率型运算放大器:运算放大器的输出电压主要受供电电源的限制。

可编程控制运算放大器:在仪器仪表得使用过程中都会涉及到量程得问题.为了得到固定电压得输出,就必须改变运算放大器得放大倍数。

运算放大器的工作原理

运算放大器具有两个输入端和一个输出端,如图1-1所示,其中标有“+”号的输入端为“同相输入端”而不能叫做正端),另一只标有“一”号的输入端为“反相输入端”同样也不能叫做负端,如果先后分别从这两个输入端输入同样的信号,则在输出端会得到电压相同但极性相反的输出信号:输出端输出的信号与同相输人端的信号同相,而与反相输入端的信号反相。

运算放大器所接的电源可以是单电源的,也可以是双电源的,如图1-2所示。运算放大器有一些非常有意思的特性,灵活应用这些特性可以获得很多独特的用途,总的来说,这些特性可以综合为两条:

1、运算放大器的放大倍数为无穷大。

2、运算放大器的输入电阻为无穷大,输出电阻为零。

现在我们来简单地看看由于上面的两个特性可以得到一些什么样的结论。

首先,运算放大器的放大倍数为无穷大,所以只要它的输入端的输入电压不为零,输出端就会有与正的或负的电源一样高的输出电压本来应该是无穷高的输出电压,但受到电源电压的限制。准确地说,如果同相输入端输入的电压比反相输入端输入的电压高,哪怕只高极小的一点,运算放大器的输出端就会输出一个与正电源电压相同的电压;反之,如果反相输入端输入的电压比同相输人端输入的电压高,运算放大器的输出端就会输出一个与负电源电压相同的电压(如果运算放大器用的是单电源,则输出电压为零)。

其次,由于放大倍数为无穷大,所以不能将运算放大器直接用来做放大器用,必须要将输出的信号反馈到反相输入端(称为负反馈)来降低它的放大倍数。如图1-3中左图所示,R1(应该是Rf才对)的作用就是将输出的信号返回到运算放大器的反相输入端,由于反相输入端与输出的电压是相反的,所以会减小电路的放大倍数,是一个负反馈电路,电阻Rf也叫做负反馈电阻。

还有,由于运算放大器的输入为无穷大,所以运算放大器的输入端是没有电流输入的——它只接受电压。同样,如果我们想象在运算放大器的同相输入端与反相输入端之间是一只无穷大的电阻,那么加在这个电阻两端的电压是不能形成电流的,没有电流,根据欧姆定律,电阻两端就不会有电压,所以我们又可以认为在运算放大器的两个输人端电压是相同的(电压在这种情况就有点像用导线将两个输入端短路,所以我们又将这种现象叫做“虚短”)。

常用运算放大器电路

1、InverterAmp.反相位放大电路:

放大倍数为Av=R2/R1但是需考虑规格之Gain-Bandwidth(增益带宽)数值。

R3=R4提供1/2电源偏压

C3为电源去耦合滤波

C1,C2输入及输出端隔直流

此时输出端信号相位与输入端相反

2、Non-inverterAmp.同相位放大电路:

放大倍数为Av=R2/R1

R3=R4提供1/2电源偏压

C1,C2,C3为隔直流

此时输出端信号相位与输入端相同

3、Voltagefollower缓冲放大电路:

O/P输出端电位与I/P输入端电位相同

单双电源皆可工作

4、Comparator比较器电路:

I/P电压高于Ref时O/P输出端为Logic低电位

I/P电压低于Ref时O/P输出端为Logic高电位

R2=100*R1用以消除Hysteresis状态,即为强化O/P输出端,Logic高低电位差距,以提高比较器的灵敏度.(R1=10K,R2=1M)

单双电源皆可工作

5、Square-waveoscillator方块波震荡电路:

R2=R3=R4=100K

R1=100K,C1=0.01uF

Freq=1/(2π*R1*C1)

6、Pulsegenerator脉波产生器电路:

R2=R3=R4=100K

R1=30K,C1=0.01uF,R5=150K

O/P输出端OnCycle=1/(2π*R5*C1)

O/P输出端OffCycle=1/(2π*R1*C1)

7、Activelow-passfilter主动低通滤波器电路:

R1=R2=16K

R3=R4=100K

C1=C2=0.01uF

放大倍数Av=R4/(R3+R4)

Freq=1KHz

8、Activeband-passfilter主动带通滤波器电路:

R7=R8=100K,C3=10uF

R1=R2=390K,C1=C2=0.01uF

R3=620,R4=620K

Freq=1KHz,Q=25

9、High-passfilter高通滤波器电路:

C1=2*C2=0.02uF,C2=0.01uF

R1=R2=110K

6dBLow-cutFreq=100Hz

10、Adj.Q-notchfilter频宽可调型滤波器电路:

R1=R2=2*R3

C1=C2=C3/2

Freq=1/(2π*R1*C1)

VR1调整负回授量,越大则Q值越低。(表示频带变宽,但是衰减值相对减少。)

R1,R2,R3,C1,C2,C3为Twin-Tfilter结构。

11、Wien-bridgeSine-waveOscillator文桥正弦波震荡电路:

R1=R2,C1=C2

R3与D1,D2Zener产生定点压负回授

Freq=1/(2π*R1*C1)

D1与D2可使用Lamp效果更佳(产生阻抗负变化系数)

12、Peakdetector峰值检知器电路:(范例均为正峰值检知)

本电路仅提供思维参考用(右方电路具放大功能)

Eo=Ei*(R4+R3)/R3

S1为连续取样开关,因应峰值不断的变化。

13、Positive-peakdetector正峰值检知器电路:

R1=1K,R2=1M,C1=10uF

只有在I/P电位高于OP-端电位时,才能使Q1导通,O/P电位继续升高.

正峰值必须低于电源正值,所得数据为最高值。

14、Negative-peakdetector负峰值检知器电路:

R1=1M,C1=10uF

只有在I/P电位低于OP-端电位时,O/P电位继续降低.

负峰值必须高于电源负值,所得数据为最高值。

15、RMS(Absolutevalue)detector绝对值检知器电路:

不论I/P端极性为何,皆可由O/P端输出,若后端再接上正峰值检知器电路,即可取得RMS数值。

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