Abstract: MATLAB software platform is used to study the performance of the fifth order IIR digital low-pass filter designed by bilinear transformation method. The relationship between the order of digital filter and the maximum attenuation of passband, the minimum attenuation of stopband, the corner frequency of passband boundary and the corner frequency of stopband boundary is derived. At the same time, the transition band and stop band of the filter are further analyzed by combining the system function, z-domain analysis and simulation results. Analysis indicates that: the fifth order IIR digital low-pass filter is a stable system, the phase presents delay in the passband and stopband. When the frequency is 0.25π rad/s, the phase state has reverse mutation, and the transmitted signal envelope collapses and enters the transition band. At this time, the phase presents a leading state. When the amplitude response in the stopband decays to 0, the system signal still has phase change, and  there is still signal in this frequency band.

Key words: digital filter, Matlab, reverse mutation, signal processing, IIR