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ADG725 - input RC filter creates offset

Question asked by krzysie_jrd on Aug 12, 2016
Latest reply on Aug 16, 2016 by krzysie_jrd

Hi,

 

We're using ADG725 to multiplex 16 differential Wheatstone bridge inputs, before ADG726 input we placed differential RC low pass filter to reduce high frequency noise. Output from the multiplexer goes directly to high-resolution Sigma-Delta ADC converter. It seems that the capacitors C1-C3 (please find the schematic attached) creates high offset of around 20 mV an when we remove these capacitors offset drops to around 0 mV as expected.

 

Can you please suggest what we're doing wrong here and why capacitors in combination with multiplexer causes ~20 mV offset? We have 3 additional inputs connected directly to the ADC (without multiplexer) and these inputs works without any problem with RC LPF in place.

 

Many thanks,

Krzysztof

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