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LPF Before MUX in Data Acquistion System

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Amr Wael

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Hello ,
I am designing LPF before a multiplexer in a daq , the purpose of the design is for elimenating noise not for Anti-aliasing since I am going to use a sampling frequency that is fast enough with respect to the signal's frequency.For this reason , I have selected my cut off frequency based on the input signal frequency not the sampling frequency but my question is when designing the passive Filter components should I take into consideration the output impedance which corresponds to the Rds on of the MUX 450 ohms?
Thank you very much in advance.
 

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I presume, you understand that in case of a muxed system, the critical parameter is mux rate per input, not ADC sampling rate. Nyquist criterion (if required at all) has to be fufilled per channel and LPF in front of the mux is the only way to perform anti-alias filtering.

It's not obvious how the mux series resistance relates to filter "output impedance", but it should be surely considered, as well as the ADC input impedance.
 

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