Electronics > Projects, Designs, and Technical Stuff
limitation of opamp in the single supply differential mode
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Ian.M:

--- Quote from: gf on April 11, 2019, 09:02:20 pm ---Such a divider leads to a modest PSRR wrt. the +3.3V supply rail, though.

--- End quote ---
Yes.  That's the price you pay for trying to do too much with just one  single supply low voltage OPAMP.   

If the 3.3V rail (or bias supply) isn't clean, your signal is going to get FUBARed unless you can cancel out the noise in further processing, e.g if the next stage also uses a matching divider to set its reference voltage.  Otherwise, you'd do better returning the bottom end of a single Rg to a properly stabilised and filtered low impedance reference voltage that's within the rails with enough room for your amplified signal swing above and below it.
StillTrying:
If you've got the op amps +Ve input AC de-coupled to the 0V and its -Ve input AC coupled to the +12V you're just x100 amplifying the noise of the 12V supply.

Old thread. "www.eevblog.com/forum/projects/lf357-opamp-replaced-by-an-ad797-subsititude-must-work-better-but-it-dosn't!!!/msg1503595/#msg1503595"
Zero999:

--- Quote from: StillTrying on April 11, 2019, 12:36:57 pm ---It's not very differential, we've been here before. :)

--- End quote ---
I'm not sure it's supposed to be a differential amplifier, despite the thread title.

I thought it was just an inverting amplifier, AC coupled to a signal floating at 12VDC, with the op-amp run off 3.3V.
Ian.M:
Read the other thread (and  :-- to O.P. for not mentioning this is a followup  >:( ).  You've been there before!

If the O.P. has to use a ground-referenced low voltage OPAMP doing it with anything other than a gated precision differential amplifier configuration will be like listening for a mouse fart in a hurricane.  He's interested in mV or uV  level signals immediately after a 1.9V pk-pk pulse.   That's going to make life interesting (in the Chinese curse sense).
VanitarNordic:

--- Quote from: Ian.M on April 12, 2019, 08:23:03 am ---Read the other thread (and  :-- to O.P. for not mentioning this is a followup  >:( ).  You've been there before!

If the O.P. has to use a ground-referenced low voltage OPAMP doing it with anything other than a gated precision differential amplifier configuration will be like listening for a mouse fart in a hurricane.  He's interested in mV or uV  level signals immediately after a 1.9V pk-pk pulse.   That's going to make life interesting (in the Chinese curse sense).

--- End quote ---

Thank you, Mr. Sherlock Holmes, for being a detector of my posts
I don't want to accept your insults, please do not reply to this thread, unfortunately, I can not remove this thread otherwise I can not stop people like you to talk like this.
I don't know how to deal with super professional designers here who fight with each other to prove their words instead of telling their technical opinion and leave.
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