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AD7190 Multiplexing

Question asked by smacleod on Jan 9, 2013
Latest reply on Jan 13, 2013 by J.Gealon

Looking for some verification on the effects of multiplexing Delta-Sigma ADCs like the AD719x series.  My understanding is that multiplexing effectively reduces the bandwidth of a signal that may be acquired while allowing a wider bandwidth of noise to be aliased through.  For instance, suppose I use the AD7190 at the maximum 4800SPS rate, with the Sinc4 filter, chopper disabled, and auto sequencing through 4 channels.  My per channel data rate will be approximately 300SPS, thus allowing un-aliased acquisition of signals on each channel up to 150SPS.  But the ADC filter response (sinc4) has a -3dB point of roughly 1100Hz (0.23 * 4800).  Thus any noise or extraneous signals from 150Hz up to 1100Hz will be aliased through, pretty much unattenuated - less so at the higher frequencies.  So to reject noise beyond 150Hz, I will need to add an input filter with a break frequency somewhat lower than 150Hz, depending on how much noise rejection is desired. 

Any feedback appreciated.

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