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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