负反馈放大电路实验的负载效应分析

反馈网络的负载效应在《模拟电子技术》课程中一直是个教学盲点，往往导致负反馈放大电路实验中动态性能指标的实测值与理论值之间的误差超过工程允许范围。有鉴于此，本文通过建模分析了“负反馈放大电路”实验中反馈网络对基本放大电路负载效应的成因；对比分析了常用传统框图法与计及负载效应后负反馈放大电路的动态性能指标；利用实际电路对这二种方法计算的动态性能指标进行了实验检测。分析结果表明：传统框图法计算动态性能指标的误差由摒弃基本放大电路与反馈网络之间的关联性引起；基本放大电路与反馈网络之间的关联性通过H参数电阻形成的负载效应实现；计及负载效应能够有效消除负反馈放大电路动态性能指标的计算误差,对模拟电子技术课程的理论和实践教学具有指导意义。

Analysis on Loading Effect in Negative Feedback Amplifying Circuit Experiment

The feedback-network loading effect has been a teaching blind spot in the course of analog electronics technology, it often causes the error between measured value and theoretical value of dynamic performance index in negative feedback amplifying circuit experiment to exceed allowable engineering range. As a result of that, this paper analyzed the cause of feedback-network loading effect on basic amplifying circuit in negative feedback amplifying circuit experiment by modelling. The dynamic performance indexes of negative feedback amplifying circuit considering loading effect were compared with the ones considering the traditional block diagram structure. The indexes calculated by the two methods were checked by experiments. Results reveal that error of dynamic performance indexes calculated by traditional block diagram structure is caused mainly by discarding correlation between basic amplifying circuit and feedback network. The correlation between them is achieved by the loading effect formed by the H-parameter resistor. By considering the loading effect, computational error of the dynamic performance indexes of the negative feedback amplifying circuit can be eliminated effectively.