课程模拟电子技术论文
院系：物电学院
专业：自动化
班级：1211自动化
学生姓名：XXX
学号：XX
任课老师：XXX
2015年10月9日
Negative Feedback Amplifying Circuit of Analog Electronic
Technology
Qin Hongtao
Hubei University of Arts and Science,P.R.china,441053
1106955858@
Abstract:this paper introduces the basic conception of negative feedback amplifying
circuit,talking about the negative feedback’s type,function and importance.
Key words:negative feedback amplifying circuit ,amplification factor,effect of circuit.
1 Introduction
In 1934,the first article on negative feedback technology to improve the importance of the paper was published ,with the wide application of nagative feedback technology,the performance of the amplifying circuit is greatly improved ,so negative feedback is very important in electronic technology ,almost all of the amplifying circuits are used for negative feedback. For the diversity of the function of negative feedback amplifier,we should know the function of different kinds of negative feedback
2 Methods and Materials
2.1 Definition of negative feedback
The so-called feedback is part or all of the output of the amplifier echo to the amplifer input
circuit ,through the network,and participate in the input cortrol of the amplifier with input signal,to improve the performance of the amplifier. When the input signal is superimposed with the feedback signal,the signal is actually added to the basic amplifier input. The input signal minus feedback signal to that the net input signal is less than the input signal ,we defined as "negative feedback".
2.2 The basic block diagram
The feedback amplifier contains two parts, namely, the basic amplifier circuit and the feedback network.,it’s shown in Fig 1
（Fig1）
2..3 Basic equation
The amplification factor of the basic amplifier is called the open loop amplification,denoted as
A. The amplification factor of the feedback amplifier is named to the closed-loop amplification factor,denotes as A'. The feedback network is sent to the signal,and the transmission coefficient is called the feedback coefficient,denotes as F. The input is Xi ,output is Xo,feedback is Xf. So we can define some formulas(see Fig 2).
（Fig2）
3 Results of discussion
3.1 Effect of negative feedback on amplifier circuit
3.1.1 Reduce the amplification factor
By formula Af=A/1+Af we can know "1+Af" is feedback depth ,we can be concluded as following chart
（chart1）
It is obvious that amplification factor reduced.
3.2.2 Improve the stability of the amplification factor
The principle of negative feedback stabilization amplifier gain is because the negative feedback is automatically adjusted. Working environment changes (such as temperature, humidity), device replacement or aging, power supply voltage instability and other factors will lead to the instability of basic amplifier. After the introduction of negative feedback,the feedback network returns the change information of output signal to Amplifier input circuit ,so that the net input signal is also changed with the output signal to keep stable.
Normally, we measure the stability of the amplifier by using the relative change of the amplification factor.Negative feedback makes relative changes of the magnification to 1/(1+Af),it shows that the deeper the feedback, the better the stability.
4 Conclusion
In my opinion,after the introduction of negative feedback amplifier, the amplification factor is reduced, but it is important to improve the performance of the amplifier.It can overcome interference in electronic technology
5 References
[1]Li Jikai.Analog electronic technology and its application Science Press,2012:133～147。