The lectures include basic theory of signals, circuits and systems, the theory of continuous time filter design. Taking Butterworth filter design as an example, the students learn the design methods for Butterworth passive and active filter design. The designed circuits are simulated by SPICE program. For digital filter design, the students must know how to design FIR and IIR filters. The designed filters are used to remove the noise of the polluted signals, the spectrum and performance are compared before and after filtering..