3. Summary
Theoretically, all active RC filter schemes can be realized as switched-capacitor circuits by replacing resistors with a set of switches and capacitors. In practice, however, most of the schematics thus obtained are not suitable for integration, as they are too sensitive to the influence of parasitic capacitances. This is particularly true of schemes using gyrators or FDNRs (Frequency Dependent Negative Resistance) (see ). At present, only implementations based on the use of an integrator as a basic circuit are used. Two main methods exist:
operational simulation of an LC model filter using, in particular, the leap frog method (see ) ;
the production of biquadratic cells and their combination, particularly in the form of coupled structures.
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Summary
Imperfections due to active elements
Bibliography
Basic works
Analysis software
A number of analysis software packages are available, based on the principles of nodal analysis, to which refinements have been added to reduce calculation times and introduce the imperfections of active elements. Comparative analyses are available at
Examples of catalogued tours
Several manufacturers offer switched-capacitor biquadratic cells in the form of cataloged circuits. The best-known are the MF10 and LMF100 (National Semiconductor), containing two second-order biquadratic cells in a 20-pin package (DIP package) ...
Manufacturers
(non-exhaustive list)
Linear Technology
Maxim
National Semiconductor
Texas Instruments
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