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hi to all,
what should be design criteria for low pass filter with cutoff frequency of 4 hz which is used for pulse oximeter
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Filter selection normally has one chosing type, eg. maximaly flat, linear phase, equi-
ripple, pulse response, cheby, bessel, ......but in this case it seems main purpose of
filter to reject body movement and high ambient light levels.
http://personal.ph.surrey.ac.uk/~phs3ps/surj/v2/li.pdf
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3268017/
http://www.robots.ox.ac.uk/~neil/teaching/lectures/med_elec/notes6.pdf
http://www.crcnetbase.com/doi/pdfplus/10.1201/9781420050790.fmatt
Regards, Dana.
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Filter selection normally has one chosing type, eg. maximaly flat, linear phase, equi-
ripple, pulse response, cheby, bessel, ......but in this case it seems main purpose of
filter to reject body movement and high ambient light levels.
http://personal.ph.surrey.ac.uk/~phs3ps/surj/v2/li.pdf
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3268017/
http://www.robots.ox.ac.uk/~neil/teaching/lectures/med_elec/notes6.pdf
http://www.crcnetbase.com/doi/pdfplus/10.1201/9781420050790.fmatt
Regards, Dana.
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One suggestion to the image posted by Bob. Try reducing the filter gain from 0dB to some -ve value. If the filter gain is set to 0dB, you can see that there are ringing above 1. So this could saturate your filter if you do not handle your input & outputs properly. In order to avoid this, you can reduce the filter gain to a value so that step function peak is well within '1'.
Regards,
Kishore.