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RE: Opamp decoupling scheme

Posted by Ugly (A) on July 27, 2018 at 23:43:35

In Reply to: RE: Opamp decoupling scheme posted by madisonears on July 27, 2018 at 19:06:44:

I think it depends on how you plan to use it.

One possible consideration might be to optimize PSRR based on power supply topology. If you expect DM noise in the power supply use plus pin to minus pin decoupling to reject it and if you expect CM noise in the rails use caps from rail to ground to reject it.

Other considerations might be where is the load return current going? Opamps internal architecture and is the input couple more strongly to one rail or the other? where the internal poles are referenced? Is it getting used in a unipolar or bipolar circuit? Are you doing balanced in, virtual voltage (ground) referenced?

There is probably a ton more I forgot or never understood in the first place.

late Edit: I'm reading this and thinking I should definitely finish the story. My usual approach, not that I'm often if ever designing the circuitry for audio for my day job, since I'll typically put fair effort into eliminating DM noise in the supply, is to minimize power supply impedance as seen by the opamp and so this means a nice mlcc over ground plane and placed as near to the opamp power supply pin as possible in an attempt to reduce loop area/inductance for the high frequency transients. But you have to remember to manage return current, especially in, unipolar arrangements with bad grounding, to ensure stability.

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Kimber Kable

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