In our class we encountered several opamp circuits, for example, Non-inverting integrator:
or we can consider the sallen-key type high pass filter:
Question: In such circuits, are these considered as positive feedback or negative feedback, that is, can we say the input terminals of opamp can be virtual grounded or not?
Question: Also what is the use of this kind of positive feedback?
My intuition is that it depends on capacitor time constant, for large time constant the negative feedback will dominate. But for small time constant, the capacitor will get quickly charged and discharged, so positive feedback will dominate.