uoficowboy
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Hi - I tend to work on a lot of data acquisition systems that need low pass filters in front of analog inputs. Typically this looks like a one or two pole active filter going into an ADC.
My questions are as follows:
How do you determine how many poles you need? I mean, I understand that more poles will give you greater roll off (-20db/decade/pole, I believe). But is there a good way to determine what your actual needs are?
How do you determine the cutoff frequency? If you are sampling your ADC at 1KHz, does that mean you want your filter to have a 3db frequency of 500Hz (I believe that is a proper application of the Nyquist–Shannon sampling theorem?)
Lastly, how do you determine what you want your Q to be? Or, equivalently, how do you determine what you want your damping factor, seeta, to be? I mean, I know what different Q/seetas look like, but what makes the most sense for this application?
I suspect these are pretty open ended questions and probably fairly application specific - but any light you all can shine on them would be very much appreciated!
My questions are as follows:
How do you determine how many poles you need? I mean, I understand that more poles will give you greater roll off (-20db/decade/pole, I believe). But is there a good way to determine what your actual needs are?
How do you determine the cutoff frequency? If you are sampling your ADC at 1KHz, does that mean you want your filter to have a 3db frequency of 500Hz (I believe that is a proper application of the Nyquist–Shannon sampling theorem?)
Lastly, how do you determine what you want your Q to be? Or, equivalently, how do you determine what you want your damping factor, seeta, to be? I mean, I know what different Q/seetas look like, but what makes the most sense for this application?
I suspect these are pretty open ended questions and probably fairly application specific - but any light you all can shine on them would be very much appreciated!