Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts. It only takes a minute to sign up.
Sign up to join this community
I'm having some difficulty understanding why an op-amp has an exponential response even if its slew-rate is infinite?
Isn't the exponential response of the op-amp output caused by the parasitic capacitances of the internal op-amp structure (CGS, CGD, etc.). And the slew-rate is caused by output capacitance?
I'm having some trouble distinguishing the two. I always thought that the exponential response of an op-amp to a step input was due to capacitances.
Consider, when the output is slew-rate limited, the response isn't exponential, it's linear. So if there is an exponential response behavior, it has nothing to do with slew rate limiting and removing the slew rate limitation won't remove it.
Now if you study linear systems in general (such as simple RC circuits) you will see that single-pole linear systems have exponential responses (if I understand what you mean by "exponential response"). That is, the response to a step input has the form \$y(t) = A\left(1-\exp(t/\tau)\right)\$
So if you model your op-amp as a single-pole linear system it will have an exponential response. Of course the real op-amp's behavior is only approximately exponential, with the approximation being more accurate the more the op-amp acts like a single-pole linear system.
