Tham khảo tài liệu 'anatomy of a robot part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 206 CHAPTER EIGHT FIGURE 8-10 The step input response of the second-order analog filter To get the stopband down to 40 db at the Nyquist Frequency with this filter we d have to increase the sampling rate by a factor of 10 or so 3 octaves . If we concatenate 2 such analog filters we would get a 24 db per octave rolloff and it would only be something less than 2 octaves to achieve the same results 2 octaves X 24 db octave 8 db 40 db To get the stopband down 40 db at the Nyquist Frequency with this filter we d have to increase the sampling rate by a factor of or so 2 octaves - . This would be a good trade-off since the analog filters are relatively inexpensive and the DSP filters can be expensive depending on the technology used. If we concatenate 3 such analog filters we would get a 36 db per octave rolloff and it would only be something more than 1 octave to achieve the same results 1 octave X 36 db octave 4 db 40 db To get the stopband down 40 db at the Nyquist Frequency with this filter we d have to increase the sampling rate by a factor of or so 1 octave . This too would be a good trade-off. Details about analog filters can be found at http purdic and at guide . DIGITAL SIGNAL PROCESSING DSP 207 DSP FILTERS There s no reason not to make an antialias filter using DSP techniques. We ll be discussing how to synthesize a DSP filter next. Here are some good web sites and a PDF file covering antialiasing filters pdf appnote http danelle arpa_0697 http timhoop D A Effects Sinc Compensation At the output of the DSP system the D A generates an output stream of analog values. The D A only outputs a series of analog values that look like a rectangular staircase of constant voltages. Thus the D A inherently alters the output signal .
