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模拟法设计高阶有源滤波器已被公认有效。其明显好处是高阶有源滤波器可以从相对应的 LC 原型电路直接获得,而且保持了 LC 原型电路低敏感度的优点。有源滤波器模拟设计方法有两类:一类是元件直接模拟,另一类是运算模拟。信号流图法属于运算模拟。这里介绍的设计方法简便之处在于,它可以先将一个高阶 LC 梯形滤波器分解为典型的单元电路,每一单元电路有一与之对应的(模拟)信号流图,将这些图连接即得到滤波器完整的信号流图。信号流图每一支路再用典型的运算放大器积分电路一一代换,元件值接着就可计算出来。显然,这里不须要列出繁多的线性方程组,不须要考虑这些方程组形式是否合适,以避免出现微分电路。方法便于掌握,不容易出差错,电路清晰,调整方便。
Analog design high-order active filter has been recognized as valid. The obvious advantage is that high-order active filters can be obtained directly from the corresponding LC prototype circuit while maintaining the low sensitivity of the LC prototype circuit. There are two types of active filter simulation design methods: one is direct simulation of components, and the other is analog computation. Signal flow graph method is a computational simulation. The simplicity of the design method introduced here is that it can first decompose a high-order LC ladder filter into a typical unit circuit with an (analog) signal flow map for each unit circuit, connecting these graphs to get Filter complete signal flow diagram. Each branch of the signal flow diagram is then replaced by a typical operational amplifier integration circuit, and the component values can be calculated. Obviously, there is no need to list a large number of linear equations here, and it is not necessary to consider whether the form of these equations is suitable to avoid the differential circuit. The method is easy to grasp, not easy to go wrong, the circuit is clear, easy to adjust.