I am new on digital filter, hopefully I can get some intuitive insights here. So, here is the question:
A low pass filter with 5Hz cut-off frequency is to be designed. The signals presented have maximum frequency of 1kHz. Therefore a 1MHz sampling rate will fully satisfy the Naquist Sampling theory for the digital filter part.
Say I want to implement a 5Hz analog low pass filter, I need to wait at least 0.2s, or even 10 times more time, to get one accurate data, because of the charging time of RC circuits.
Are things the same for digital filters? Say I want to implement a 10 tap(data length) low pass filter with cut off frequency 5Hz. The sampling rate is 1MHz. Can I get a valid data within 1/(1MHz/10) = 10us time? That seems not very reasonable to me....
In this application, two filters are to be designed.
In both filters, we only want to know the DC. The DC signal is buried in large noises. A cutoff frequency of 5Hz is chosen, since we want to have valid readings at 5Hz. And lower cutoff frequency means smaller noises, but also longer time needed to get an appropriate reading.
One filter has bandwidth of 6kHz(not 1MHz, which was just an example). And we are planning to over sample it with sampling rate of 36kHz. The other one filter has bandwidth of 60Hz, and we are planning to over sample it at 1kHz.
As can be observed from the filter description, we want lower noises, as low as possible. Therefore the digital filters are expected to have sharp edge at 5Hz. And all other parameters, such as "linear phase, small ripple.. and etc" are not important to us, since we only care about DC readings.
And, I am quite confused by the enormous types of digital filters.. How to choose them? Say, between FIR and IIR?