Analog Filters

A filter is used to discriminate unwanted signals in a complex measurement signal. This chapter first introduces passive filters (RCL filters) of first and second order. Next, biquad filters, switched capacitor filters, and state-variable filters are introduced. The quality factor is defined (the Q factor) and different filter characteristics and filter models (Butterworth, Chebyshev, and elliptic models) are illustrated. Analog filters can be implemented using so-called Sallen–Key links. Section 9.6 demonstrates how a given filter characteristic can be transformed into any other filter characteristic. To process the signal in time space, it is necessary to introduce a mathematical operation called convolution (Sect. 9.7). Like transforms, convolution is usually considered to be hard to grasp by students, but this chapter emphasizes the understanding of convolution by using graphical examples.