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(二)简单二阶电路 |
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其中 |
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由幅频特性可见ω>>ω0时衰减的斜率为－40dB/十倍频。但在ω0附近，其幅频特性与理想的低通滤波特性相差较大。 |
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将电容C1的接地端改接到集成运放的输出端。只要参数合适: |
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(1)该电路在f0附近形成正反馈，不致造成自激振荡，使f0附近的电压放大倍数得到提高。
(2)当ω<<ω0时，电容C1阻抗大，反馈信号较弱，对电压放大倍数影响不大。
(3)当ω>>ω0时，输入信号被C2衰减，输出电压的幅值小，反馈信号较弱，对电压放大倍数影响不大。 |
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(1)当ω<<ω0时，Af(ω)/Af=1,
即 20lg[Af(ω)/Af]=0dB |
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(2)当ω=ω0时，Af(ω)/Af= ,幅值下降了3dB,ω0是电路的通带截止角频率 |
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(3)当ω=10ω0时， |
说明阻带区内 |
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Af(ω0)以每十倍频40dB(100倍)的速率衰减。 |
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(4)Q大小主要影响Af(ω)在ω0附近的情况，Q值越大，Af(ω0)越大。 |
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