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Bias on LPF Input - Required?

Question asked by groger on Aug 5, 2014
Latest reply on Aug 6, 2014 by Matt.Duff

Hi,

 

I used ADI's filter wizard to generate a 10th order LPF, of 0dB gain. Please see attachment WIZ_LPF.jpg  that shows the first stage, and a bit of the next. Inverting or non-inverting is OK, the wizard created a non-inverting. I also have the requirement of a single power supply of 3.3V

The objective is to couple a sensor to the input that is a non-powered, ground referenced sensor with low frequency signals (< 50Hz)

 

I'm thinking that it's possible to just use a capacitor to couple the input to R1E, but somehow that doesn't seem correct. What about op-amp bias? In ADI's technical notes, I found the second attachment - OPAMP_REF.jpg - that isn't quite the same, as that circuit is a gain stage and perhaps requires the Vdd/2 reference?

 

Thanks for any explanation that could clarify.

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