I'm having a problem with my AD8426 instrumental amplifier design. As I show in the image, I use a 3.3 V supply and after increasing my input signal, I use 1.8V virtual ground to make it oscillate on 1.8 V.
However, since Vout oscillates above 1.7395 V, the next stage increases the voltage difference between Opamp 1.8 and 1.7395. Since this does not comply with the operating conditions of the LTC 2068, I see a flat output above 3.29 at the opamp output.
I solved the problem experimentally by putting a capacitor (C17) at the inamp output, but I do not know how accurate this will be in an EEG application.
Is there a way to overlay the AD8426 output to exactly 1.8 V? Or the method I applied (placing a capacitor C17) is okay?
No capacitor (c17) out
out with C17