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5. Production of complex active filters
Complex active filters can be created by combining biquadratic cells or simulating an LC filter.
5.1 Simple cascade of biquadratic cells
For low-order filters (up to 8, for example), with a bandwidth B that's not too small (order of magnitude: B > 20%), synthesis by simple cascading of biquadratic cells is suitable. In this case, the Q coefficients of the cells remain low or moderate (Q < 10 to 15, for example), and sensitivities remain acceptable. The design is very simple, and the independence of the individual cells facilitates adjustment.
Three precautions should be taken in practice:
ensure that the cascading order preserves the filter's dynamic range: high leading Q for weak signals...
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Production of complex active filters
Bibliography
References
Software
The calculation of an active filter is divided into two distinct parts:
transfer function calculation ;
calculation of the numerical values of the elements included in the production diagram.
Filter transfer functions can be calculated using general mathematical software such as MATLAB, Mathematica or Mathcad,...
Manufacturers, constructors
Analog Device http://www.analog.com/
Burr Brown (see Texas Instrument)
Linear Technology http://www.linear.com/
Maxim http://www.maxim-ic.com/
...
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