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limitation of opamp in the single supply differential mode
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Zero999:
The link was broken. Here's the correct one.
https://www.analog.com/media/en/technical-documentation/data-sheets/AD8223.pdf

The AD8223 is a good idea. Its common mode range goes to 150mV below the negative rail, so if the peak supply ripple + signal is under that, both inputs can be biased to 0V via suitable resistors, say 1M to 10M and the input AC coupled to each input, via a capacitor.
SiliconWizard:
I've used an AD8223 for a thermocouple amplifier on a 3.3V single supply and it's great.

I suggest still checking that you're using it in its operating range. The datasheet will help, you can also use this tool: https://www.analog.com/designtools/en/diamond/#difL=-0.08&difR=0.08&difSl=-0.08&gain=100&l=-6&pr=AD8223&r=6&sl=-6&tab=1&ty=1&vn=-10&vp=10&vr=0

You may have to use a Vref > 0.
VanitarNordic:

--- Quote ---Anyway, back on topic. The op-amp should be run off the 12V rail. An AC coupled differential amplifier could be used.
--- End quote ---

so you confirm my word that when the sensor is VCC referenced (+12V), then the opamp should be at least 12V and a 3.3V opamp cannot do the best job
gf:

--- Quote from: VanitarNordic on April 12, 2019, 02:34:52 pm ---
--- Quote ---Anyway, back on topic. The op-amp should be run off the 12V rail. An AC coupled differential amplifier could be used.
--- End quote ---

so you confirm my word that when the sensor is VCC referenced (+12V), then the opamp should be at least 12V and a 3.3V opamp cannot do the best job

--- End quote ---

What is the peak-to-peak voltage swing at the 12V level?
a) common mode (-> basically the power supply ripple which you do not want to get amplified)
b) differential (the sensor signal itself which should be amplified)

And is AC coupling OK? You do not need DC coupling, do you?
gf:

--- Quote from: SiliconWizard on April 12, 2019, 01:57:45 pm ---You may have to use a Vref > 0.
--- End quote ---

Sure, if the input is AC coupled, then it is definitively necessary to set an output offset > 0 in order to avoid clipping of the negative lobes.
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