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Question about anti aliasing

hello

i have some little questions to ask to the more experienced users...

In lots of designs with adc's i see that anti aliasing filter is missing ... it's normal? For example , i want to sample a 500Hz signal ( i expect to do make a ecg maybe in the future ) , it's mandatory to put an anti aliasing filter or i can live without it ? ( i mean putting in 8 filters it's so boring ^^ , otherwise i can put a standalone adc and analog mux to share the filter ... taking care off course of the switching transitions ...

Or, instead of that could i do it all digital (dsp or messy loop) one inside my mcu ??

( i was thinking of doing a 60hz notch inside but can i use it too to perform the antialiasing AFTER sampling???)

Can the CMSIS libraries do it and will they work in uvision?

this part is a little bit confusing to me.

thanks for your help to understand better this obscure part ...

Parents
  • Your need of a low-pass filter is directly related to the frequency range the input signal can have compared to the sample rate you run the ADC at.

    If you know you always sample at way higher frequency than any any frequency component of your signal, then you can ingnore the low-pass filter and only settle for traditional protection circuitry.

    If the input frequency can be too high, then you need a low-pass filter to subpress that frequency - without the filter, you will get falting where the high frequency will be sampled as a lower frequency. And you can't use any software to filter away incorrectly sampled input data.

    But the specification should be very clear what frequency range you _must_ be able to sample within a maximum error tolerance. And that specification must also contain information if you have other signal energies that must be filtered away.

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  • Your need of a low-pass filter is directly related to the frequency range the input signal can have compared to the sample rate you run the ADC at.

    If you know you always sample at way higher frequency than any any frequency component of your signal, then you can ingnore the low-pass filter and only settle for traditional protection circuitry.

    If the input frequency can be too high, then you need a low-pass filter to subpress that frequency - without the filter, you will get falting where the high frequency will be sampled as a lower frequency. And you can't use any software to filter away incorrectly sampled input data.

    But the specification should be very clear what frequency range you _must_ be able to sample within a maximum error tolerance. And that specification must also contain information if you have other signal energies that must be filtered away.

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