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1、反馈的基本概念 |
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本节讲授的基本概念有:反馈、正反馈、负反馈、交流反馈、支流反馈。
负反馈放大电路的四种类型是:电压串联负反馈、电压并联负反馈、电流串联负反馈、电流并联负反馈。
用“瞬时极性法”判断反馈的极性;用输出端“短路法”分析是电压负反馈,还是电流负反馈。 |
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2、负反馈放大器的基本关系式 |
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根据负反馈放大器方块图表示,开环放大倍数为 |
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反馈系数为 |
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闭环放大倍数为 |
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其中 |
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称为反馈深度。在深度负反馈条件下,有 |
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3、负反馈对放大电路性能的影响 |
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(1)提高放大倍数的稳定性,具体关系如下: |
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(2)扩展放大器的通频带,加负反馈前后上限频率之间和下限频率之间的关系分别为 |
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(3)减小放大器非线性和内部噪声的影响。 |
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(4)对输入电阻和输出电阻的影响是:串联负反馈增大放大器的输入电阻,并联负反馈减小放大器的输入电阻;电压负反馈稳定输出电压减小输出电阻;电流负反馈稳定输出电流,增大输出电阻。 |
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4、基本运放构成的基本负反馈放大电路 |
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在理想情况下,集成运放具有如下特点: |
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虚短 U-=U+
虚断 I-=I+=0 |
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利用这两个特点,分析集成运算放大器组成的比例、加、减、积分、微分、对数和反对数运算电路,以及输出电压与输入电压关系的求法。介绍了电流—电压变换器的工作原理。 |
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5、负反馈放大器的自激问题 |
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主要介绍了集成运算放大器的频率特性,产生自激振荡的原因和条件,以及消除自激的两种方法:滞后补偿、超前-滞后补偿。 |
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