hi to all,
what should be design criteria for low pass filter with cutoff frequency of 4 hz which is used for pulse oximeter
What's about this?
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'.
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.