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Why is this MFB filter oscillating?

Question asked by bhennink on Mar 9, 2018
Latest reply on May 3, 2018 by bhennink

Hi

I haven't used differential ams a lot but in the past so maybe I try to do something I should not.

I created a 2nd order MFB lowpass filter that I need in my design.

I wonder, why is this circuit oscilating at about 180 MHz if I do not add C5 at the output?

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And this is not only oscillating with this part but also with a TI diffamp so I think it has to do with the topology of this MFB design.

With C5 added the circuit is quiet (also over temperature with multiple sample boards).

I would like to understand at first why this starts oscillating (without C5) and stops oscilating when adding C5 so I can be sure the circuit is alway stable.

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