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Practical caveats or low frequency high-pass filters

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kender

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Folks,

Are there any practical caveats to filters with low time constant?

My signal of interest is 0.05Hz (50mHz). I want to AC couple it (into the OpAmp with input impedance of 10^13 Ohm) to remove the DC offset (introduced by the InAmp). I’ve made a 1-pole high-pass with ceramic 4.7uF and 10M. Its calculated cutoff frequency is 3mHz, but I suspect that it’s attenuating the 50mHz signal too.

Best,
Nick
 

kender

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brmadhukar said:
what are the tolerances?
The cap is X5R ceramic, which gives 20% tolerance.
The resistor is 5%.
Thanks for the advice to look at the tolerances, but even if they both stacked up the wrond way, I shouldn't get the cutoff frequency above my signal frequency.
 

arefeidi

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Hope I didn't misinterpret your question - but well, with your calculated cut off frequency at 3mHz and your signal at 50mHz there is more than one decade between the frequencies - there shouldn't be a noticeable attenuation of your 50mHz signal. Attenuation will be in the range of a few 1/100dB I suppose, nearly nothing.
 

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