5. Implementation
The designer can choose between two implementation methods.
Catalogued circuits: several manufacturers supply either biquadratic cells, such as the MF 10, whose parameters are adjustable by external resistors, or ready-made filters, whose cutoff frequency is programmable by the external clock. SGS-Thomson Microelectronics, for example, offers low-pass Cauer filters of order 5 or 7, with a bandwidth ripple of 0.1 dB, and a cut-off frequency adjustable from 10 Hz to 20 kHz by the external clock. Other manufacturers offer similar products, including AMI, National Semiconductor and Texas Instruments. These affordable devices are suitable for small to medium-sized production runs. Their use should increase thanks to the programmability of cutoff frequencies, a completely new property in analog circuitry.
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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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