CHAPTER 8

Designing Lowpass and Highpass Filters

8.1  Designing Real Filters

In Chapter 7 we saw how just about any filter you can dream up can be implemented by cascading first- and second-order filter blocks. In this chapter we look at the best ways to turn those theoretical blocks into reality. There are many ways to do this, but for the moderate Q values normally required, the two simplest and the best methods are the well-known Sallen and Key configuration and the multiple-feedback (MFB) configuration.

All the filters in this chapter have been designed with a cutoff frequency of 1 kHz, which allows quick comparisons and quick scaling of the examples to get the filter frequency you want. The use of the term “cutoff” might be taken to imply ...

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