EDIT: (problem definition shortened into 2 sentences)
For anyone using EVAL_AD7984_PMDZ and having troubles to apply -2.5, 0, 7.5 [V] and signal to differential probes, because the voltage source and signal source shares ground (then there is 2.5 [V] difference between the two), check the last comment for solution.
I got differential ADC EVAL_AD7984_PMDZ (page 17 connection) on ZedBoard working just fine (from -5 to 5 [V]). It requires not only 3.3 [V] from PMOD connection (logic) but also -2.5, 0, 7.5 [V] from external power source (Laboratory DC Power Supply - 2 adjustable outputs, that I have connected in series, thus I have "ground" on the middle pin, while on the other 2 pins there is -2.5 and 7.5 - relative to my "ground").
And here it comes, when I introduce input from another Laboratory DC Power Supply, the readings are fine within whole range.
But when I introduce signal from AFG-2125 Arbitrary Function Generator, there is offset of 2.5 [V] from both of the ADC input pins and it kind of messes up whole measurement that is below 2.5 [V].
May I get a little bit of insight on that ?
The ground of the ADC probes is the "ground" mentioned above.
Technically I have 3 grounds:
- ZedBoard (and thus PMOD connection)(powered from its own power source)
- External power source for the ADC (with the "ground")
- Signal Generator ground
I am not sure how to resolve that. Would it help if the Signal Generator was battery powered ?
(I am sorry if some electrical engineer finds the above schematic offensive)
Schematics for EVAL_AD7984_PMDZ