The essential skill for understanding opamps is to accept this sequence of assumptions and simplifications. The difference is too small for almost all instruments. If you build this opamp circuit on your bench and try to measure v+ - v- your meter or scope will register 0v. That 2 microvolt difference is enough to make the opamp generate the expected 2V output. This difference is represented exactly by A/(A+1). The difference may be perhaps 2 microvolt. So, voltages at the input to the opamp are super close, but not exactly identically equal. We then simplified the gain expression by allowing that A/(A+1) term to be exactly 1. ![]() ![]() Remember in a previous video we developed an accurate gain expression that included a term like A/(A+1)? If the gain "A" is huge, then A/(A+1) is VERY close to 1. The speed an accuracy of the correction is the "dynamic" performance of the opamp circuit.ΔΆ:10 is not exactly precise. In this case, the feedback network flexes its muscles and drives this new big error back to zero as quick as it can. You've caused an intentional change to the set point and the error signal (v+ - v-) can be very big. The next interesting case is what happens when vin changes suddenly. This is a continuous process in an analog opamp, you don't see little discreet steps, just a continuous attempt to match the set point. You hope each successive correction is smaller than the previous, so the output converges on the right value. This is the tiny wiggle you are asking about. In that case, the feedback network has a new "incorrect" Vo to work with, and it generates a new correction. In a real-world opamp circuit the correction might not be perfect (due to small internal voltage flaws, or time delays inside the opamp). In an ideal circuit the correction would be perfect and the right Vo would be restored immediately. The ideal magnitude of the correction (the size of the little arrow) is exactly the right size to perfectly correct the deviation. The negative feedback network (R1 and R2) is arranged to drive v- back in the direction of v+. Suppose Vout wanders off in some direction for any reason (gain flaw, temperature change). ![]() The purpose of the opamp and resistors is to drive Vo to the value it needs to be to make v- match the input set point, v+. Let's call the voltage input vin the "set point" for the circuit. When the input is unchanging, this wiggle is so small you can't see it on an oscilloscope. You are correct that the output will wiggle around the desired (nominal) Vo value.
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